















                             TUCSON AMATEUR PACKET RADIO

                                     Packet Radio

                               Terminal Node Controller

                                     TNC 2, Rev 2



                                    SYSTEM MANUAL


                           Including Command Reference for
                                Firmware Version 1.1.8








          Tucson Amateur Packet Radio                   TNC 2 System Manual




                         Copyright (c) 1985, 1990, 1991, 1992
                       Tucson Amateur Packet Radio Corporation
                                    P.O. Box 12925
                                Tucson, AZ  85732-2925

                                    (602) 749-9479
                                  FAX (602) 749-5636

                                 All rights reserved.

          Reproduction  or translation of any part of this work beyond that
          permitted  by Sections  107  or 108  of  the 1976  United  States
          Copyright  Act  (or  its  legal successor)  without  the  express
          permission  of the  copyright owner is  unlawful except  as noted
          below.    Requests  for   permission  to  copy  or  for   further
          information should  be addressed  to Tucson Amateur  Packet Radio
          Corporation.

          Except  as  noted above,  permission  is  hereby  granted to  any
          non-profit  group or individual to  reproduce any portion of this
          document provided that: the reproduction  is not sold for profit;
          the  intent  of  the   reproduction  is  to  further  disseminate
          information  on packet  radio; the reproduction  is not  used for
          advertising  or  otherwise   promoting  any  specific  commercial
          product;  and full credit is given to Tucson Amateur Packet Radio
          Corporation  (including  address)  as   the  original  source  of
          information.


                                  August 1985



                  TNC 2 SOFTWARE SOURCE CODE and TNC FIRMWARE
                               Copyright (c) 1985
                                     Systek
                              All rights reserved.

          Reproduction  or translation of any part of this work beyond that
          permitted  by Sections  107  or 108  of  the 1976  United  States
          Copyright  Act  (or  its  legal successor)  without  the  express
          permission  of the  copyright owner  is unlawful except  as noted
          below.    Requests   for  permission  to  copy   or  for  further
          information should  be addressed  to Tucson Amateur  Packet Radio
          Corporation.



                                          ii








          Tucson Amateur Packet Radio                   TNC 2 System Manual




























                                    FOURTH EDITION

                                         1992

          The  information contained  in this  document has  been carefully
          checked and is  believed to  be entirely reliable.   However,  no
          responsibility  is  assumed  for inaccuracies.    Tucson  Amateur
          Packet  Radio  Corporation  (TAPR)  reserves the  right  to  make
          changes  to  any products  to  improve  reliability, function  or
          design  without obligation  to purchasers of  previous equipment.
          TAPR does not assume any liability arising out of the application
          or use of any  product or circuit described herein;  neither does
          it convey  any license under its  patent rights or the  rights of
          others.










                                         iii








          Tucson Amateur Packet Radio                   TNC 2 System Manual

                                  TABLE OF CONTENTS


          ACKNOWLEDGMENTS                                               vii

          Chapter 1  INTRODUCTION                                         1
               What is TAPR?  . . . . . . . . . . . . . . . . . . . . .   1
               First Steps  . . . . . . . . . . . . . . . . . . . . . .   2

          Chapter 2  COMPUTER INTERFACING                                 3
               Serial Port Signals  . . . . . . . . . . . . . . . . . .   3
                    Apple Macintosh . . . . . . . . . . . . . . . . . .   5
                    Commodore 64 or VIC-20  . . . . . . . . . . . . . .   5
                    IBM PCjr  . . . . . . . . . . . . . . . . . . . . .   5
                    Radio Shack Color Computer  . . . . . . . . . . . .   6
                    Radio Shack Model 100 and NEC 8201  . . . . . . . .   6
                    Other Computers with 25-pin RS-232C Ports . . . . .   6
                    Other Computers with Nonstandard Serial Ports . . .   7
               Software Requirements  . . . . . . . . . . . . . . . . .   8
                    Apple Macintosh . . . . . . . . . . . . . . . . . .   8
                    Commodore 64 or VIC-20  . . . . . . . . . . . . . .   8
                    IBM PCjr  . . . . . . . . . . . . . . . . . . . . .   8
                    Radio Shack Color Computer  . . . . . . . . . . . .   9
                    Radio Shack Model 100 and NEC 8201  . . . . . . . .   9
               Verifying Serial Port Operation  . . . . . . . . . . . .   9
               TNC 2 Serial Port Pin Functions  . . . . . . . . . . . .  10

          Chapter 3  RADIO INTERFACING                                   12
               Method 1:  Direct Connection to Microphone and Speaker .  13
               Method 2:  Accessory Jack or Interface Box Connection  .  14

          Chapter 4  OPERATION I:  GETTING STARTED                       17
               First Steps  . . . . . . . . . . . . . . . . . . . . . .  17
                    Entering Commands . . . . . . . . . . . . . . . . .  18
               Serial Port Configuration  . . . . . . . . . . . . . . .  19
                    Parity and Word Length  . . . . . . . . . . . . . .  20
                    Echos . . . . . . . . . . . . . . . . . . . . . . .  20
                    New Lines and Line Wrapping . . . . . . . . . . . .  21
               Basic Operation  . . . . . . . . . . . . . . . . . . . .  21
                    A Connecting and Disconnecting Exercise . . . . . .  21
                    Digipeating . . . . . . . . . . . . . . . . . . . .  23
                    Unsuccessful Connections  . . . . . . . . . . . . .  24
               Monitoring Channel Activity  . . . . . . . . . . . . . .  25
               Your First Packet QSO  . . . . . . . . . . . . . . . . .  27
                    Starting the QSO  . . . . . . . . . . . . . . . . .  27
                    Digipeating . . . . . . . . . . . . . . . . . . . .  28
                    Monitoring on the Air . . . . . . . . . . . . . . .  29
               Special Input Characters . . . . . . . . . . . . . . . .  29
               QRA or help for My path's fallen, and it can't get up  .  31


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 5  OPERATION II:  FURTHER DETAILS                      33
               Special Characters . . . . . . . . . . . . . . . . . . .  33
               Operating Modes  . . . . . . . . . . . . . . . . . . . .  34
                    Command Mode  . . . . . . . . . . . . . . . . . . .  35
                    Entering Data-Transfer Modes  . . . . . . . . . . .  36
                    Converse Mode . . . . . . . . . . . . . . . . . . .  37
                    Transparent Mode  . . . . . . . . . . . . . . . . .  38
               Flow Control . . . . . . . . . . . . . . . . . . . . . .  39
                    XON/XOFF Flow Control . . . . . . . . . . . . . . .  40
                    Hardware Flow Control . . . . . . . . . . . . . . .  41
                    Type-in Flow Control  . . . . . . . . . . . . . . .  41
               Packet Operation . . . . . . . . . . . . . . . . . . . .  42
                    Station Identification  . . . . . . . . . . . . . .  42
                    Automatic Operations  . . . . . . . . . . . . . . .  42
               Packet Formatting  . . . . . . . . . . . . . . . . . . .  44
               Commands Affecting Protocol  . . . . . . . . . . . . . .  44
               Packet Timing Functions  . . . . . . . . . . . . . . . .  45
                    Transmit Timing . . . . . . . . . . . . . . . . . .  45
                    Packet Timing . . . . . . . . . . . . . . . . . . .  46
                    Radio Baud Rate . . . . . . . . . . . . . . . . . .  47
                    Special Protocol Times  . . . . . . . . . . . . . .  48
               Monitor Functions  . . . . . . . . . . . . . . . . . . .  49
               Real-Time Clock and Time Stamping  . . . . . . . . . . .  50
               HF and OSCAR . . . . . . . . . . . . . . . . . . . . . .  50
               Modem Calibration using CAL and RXCAL  . . . . . . . . .  52
                    Modulator Adjustment  . . . . . . . . . . . . . . .  53
                    Demodulator Adjustment  . . . . . . . . . . . . . .  55
                    Other Considerations  . . . . . . . . . . . . . . .  55

          Chapter 6  TAPR TNC 2 COMMANDS                                 57
               Entering Commands  . . . . . . . . . . . . . . . . . . .  57
               Command List . . . . . . . . . . . . . . . . . . . . . .  58
                    COMMAND NAME  . . . . . . . . . . . . . . . . . . .  58
                    Default . . . . . . . . . . . . . . . . . . . . . .  58
                    Parameters  . . . . . . . . . . . . . . . . . . . .  58
                    Remarks . . . . . . . . . . . . . . . . . . . . . .  60
               Messages . . . . . . . . . . . . . . . . . . . . . . . . 144
                    General Messages  . . . . . . . . . . . . . . . . . 144
                    Command Mode Error Messages . . . . . . . . . . . . 145
                    Link Status Messages  . . . . . . . . . . . . . . . 146
               Health Counters  . . . . . . . . . . . . . . . . . . . . 149

          Chapter 7  HARDWARE                                           152
               TNC 2 Specifications . . . . . . . . . . . . . . . . . . 152
               General Description  . . . . . . . . . . . . . . . . . . 153
               Detailed Circuit Description . . . . . . . . . . . . . . 154
                    Oscillator  . . . . . . . . . . . . . . . . . . . . 154
                    Dividers and Baud-rate Generator  . . . . . . . . . 154
                    CPU Complex . . . . . . . . . . . . . . . . . . . . 155
                    Serial Interface  . . . . . . . . . . . . . . . . . 156

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                    Watch-dog Timer . . . . . . . . . . . . . . . . . . 156
                    Modem . . . . . . . . . . . . . . . . . . . . . . . 156
                    Power Supply  . . . . . . . . . . . . . . . . . . . 157
               RS-232C Handshaking Protocol . . . . . . . . . . . . . . 158
               Jumper Functions . . . . . . . . . . . . . . . . . . . . 159
               Modem Disconnect - J4  . . . . . . . . . . . . . . . . . 160
               Tuning Indicator Interface - J3  . . . . . . . . . . . . 163

          Chapter 8  TROUBLESHOOTING                                    165
               General Tests  . . . . . . . . . . . . . . . . . . . . . 165
                    Step 1:  Power Supply . . . . . . . . . . . . . . . 165
                    Step 2:  Obvious Problems . . . . . . . . . . . . . 166
                    Step 3:  Assembly Problems  . . . . . . . . . . . . 166
                    Step 4:  Cabling Problems . . . . . . . . . . . . . 166
                    Symptom:  TNC appears dead  . . . . . . . . . . . . 167
                    Symptom:      Modem   won't   calibrate   or   key
                         transmitter. . . . . . . . . . . . . . . . . . 168
                    Symptom:    Uncopyable  transmitted   or  received
                         packets  . . . . . . . . . . . . . . . . . . . 169
               Terminal Interface Troubleshooting . . . . . . . . . . . 169
                    Symptom:  TNC won't sign on to the terminal.  . . . 170
                    Symptom:   The TNC  appears to be  signing on  but
                         only gibberish is printed on the terminal. . . 170
                    Symptom:   The TNC  signs on  OK but  won't accept
                         commands.  . . . . . . . . . . . . . . . . . . 171

          Chapter 9  PACKET RADIO PROTOCOL                              172
               Explanation of Protocol  . . . . . . . . . . . . . . . . 172
                    Data Link Layer . . . . . . . . . . . . . . . . . . 173
               HDLC Frames  . . . . . . . . . . . . . . . . . . . . . . 173
               AX.25 Level Two  . . . . . . . . . . . . . . . . . . . . 174
               Channel Use and Timing Functions . . . . . . . . . . . . 176
               Channel Flow Control . . . . . . . . . . . . . . . . . . 178

          Appendix A  Multi-Connect Survival Guide                      180

          Appendix B  Prioritized Acknowledgment - An Overview          182
               THE IDEA . . . . . . . . . . . . . . . . . . . . . . . . 182
               THE PROBLEM  . . . . . . . . . . . . . . . . . . . . . . 182
               HOW IT WORKS . . . . . . . . . . . . . . . . . . . . . . 182
               NEW PARAMETERS . . . . . . . . . . . . . . . . . . . . . 184
               OTHER RELATED PARAMETERS . . . . . . . . . . . . . . . . 184
               INITIAL PARAMETER SETTINGS SUMMARY . . . . . . . . . . . 186

          Appendix C  Default Locations                                 187

          BIBLIOGRAPHY                                                  197




                                          vi








          Tucson Amateur Packet Radio                   TNC 2 System Manual



                                ACKNOWLEDGMENTS




          The Tucson Amateur Packet Radio Terminal Node Controller Model  2
          project was made possible through the selfless dedication of many
          individuals.    These  people  represent the  highest  ideals  of
          volunteerism  and public  service, giving  of themselves  for the
          benefit of the Amateur  Radio community worldwide.  It is on this
          basis that  TAPR exists,  and it  is on  this basis  that Amateur
          packet radio has flourished during the past few years.

          It is  not  possible to  document the  specific contributions  of
          every  participant in  TNC  2's  development,  nor even  to  list
          everyone who  made a contribution.   However, the  following list
          includes those without  whose efforts the project  would not have
          been possible.

               Peter Eaton, WB9FLW           Circuit board layout
               Howard Goldstein, N2WX        Software design
               Steven Goode, K9NG            Modem
               Charles Green, N0ADI          Documentation
               Lyle Johnson, WA7GXD          Documentation
               Daniel Morrison, KV7B         Testing
               Margaret Morrison, KV7D       Documentation
               Paul Newland, AD7I            Hardware design
               Harold Price, NK6K            Protocol

          To the  above list must be  added those who were  involved in the
          Beta Test of  the TNC 2 design:  Paul  Barnett, N0CRN; Jon Bloom,
          KE3Z; Mike Brock, WB6HHV; Tom Clark, W3IWI;  John Conner, WB0FHG;
          Terry Fox,  WB4JFI; Andy  Freeborn, N0CCZ; Eric  Gustafson, N7CL;
          Skip Hansen,  WB6YMH; Phil  Karn, KA9Q; Scott  Loftessness, W3VS;
          Hank  Magnuski,  KA6M;  Bill  Reed, WD0ETZ;  Gwyn  Reedy,  W1BEL;
          Russell Reiss, K1HOP; Jeff Ward, K8KA.

          The  TNC 2  project  would never  have  taken place  without  the
          success  of the  TNC 1  project.   In addition  to many  of those
          listed  above, the following people contributed to making TNC 1 a
          recognized  standard of Amateur  packet radio:   Mark Baker; Marc
          Chamberlin,  WA7PXW; Den  Connors, KD2S; David  Henderson, KD4NL;
          Heather Johnson, N7DZU.






                                         vii








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 1  INTRODUCTION


          Welcome to the exciting world of Amateur packet radio.   You will
          soon  be joining the ranks of the fastest growing mode in Amateur
          Radio since 2-meter FM.

          The purpose of  the Tucson Amateur  Packet Radio (TAPR)  Terminal
          Node  Controller (TNC)  is to  act as  an interface  between your
          ordinary voice radio, such as a 2-meter FM transceiver or HF  SSB
          transceiver, and  your computer.  The TNC will perform all of the
          "magic"  of establishing  error-free communications  between your
          station and another  packet-radio equipped station.  You  will be
          able to have a  "private channel" while sharing a  frequency with
          other packet  stations, "read  the mail"  or other  QSOs, operate
          remote  computer "bulletin  board" or "mailbox"  stations, handle
          message traffic --  in short, be able to enjoy all the advantages
          of digital communication techniques in your ham shack.

          Your TAPR TNC  2 is the key to your packet  station.  It is based
          on  the original  TAPR  TNC and  inherits  many of  the  advanced
          features  of that design,  coupled with the  experience gained by
          thousands of TAPR-equipped Amateur packet stations worldwide.

          This manual will be your  guide into the realm of Amateur  packet
          radio.  The  Assembly Manual will  take you step by  step through
          the construction and testing of your TNC.  You will then be ready
          to start with Chapter 2, which  explains how to connect your  TNC
          to  your  station  computer.   Chapter  3  will  instruct you  on
          interfacing the TNC to your radio and Chapters 4 and 5 will guide
          you  through packet  radio operation.   Chapter  6 is  a detailed
          breakdown  of  the various  commands  the  TNC  will  accept  and
          messages it  may report.  A description of the hardware design of
          TNC 2  and troubleshooting hints follow in Chapters 7 and 8.  The
          manual concludes with  Chapter 9,   an overview  of packet  radio
          protocol.  The Bibliography  lists sources of further information
          on packet radio.


          What is TAPR?

          Tucson  Amateur  Packet  Radio   is  a  non-profit  research  and
          development group dedicated to the advancement of Amateur digital
          communications.     Its  technical  "staff"  consists  solely  of
          volunteers who donate their time in pursuit of TAPR's goals.  TNC
          2  was  designed  by  such   volunteers.  TAPR  is  a  membership
          organization with members spread around the globe.  The quarterly
          Packet   Status  Register   carries  technical   and  operational
          information on packet radio,   Further, it is the  means by which
          TAPR  provides support for your TNC 2.   We encourage you to join

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          TAPR and share with  us in the development of this exciting mode.


                       Join the Packet Radio Revolution!



          First Steps

          Refer to the  Assembly Manual included with your  TNC 2 board and
          follow   the  directions   given.     When  you   have  completed
          construction,  continue  with  Chapter 2,  Computer  Interfacing.
          Build your TNC 2 carefully and...

                         ... happy packeting!




































                                          2








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 2  COMPUTER INTERFACING


          Before beginning this chapter, you should have assembled your TNC
          2  and verified  that the  power supply  is functioning  and that
          various of the LEDs function properly.   You will now attach,  or
          interface, your  TNC  2 to  your  station computer  or  terminal.
          Throughout this manual we  will use the term "computer"  to refer
          to the computer or terminal you use to communicate with your TNC.

          TNC 2 communicates with your computer through a serial port using
          signals  corresponding to  a  standard called  RS-232C.   Why  an
          RS-232C  interface?   Nearly every  computer in  production today
          either incorporates an  RS-232C style serial  port as a  standard
          feature, or  has one available  as an optional  accessory, either
          from the computer manufacturer or from a manufacturer of computer
          accessories.

          In order to  use the TNC  with your  computer, the computer  must
          have  an RS-232C serial port and  a program to support the serial
          port.  The  program will  typically be called  a modem,  terminal
          emulator, or communications program.

          Since there  are so  many computers  on the  market today,  it is
          impractical for this chapter to provide detailed instructions for
          each computer.   Detailed information  is given for  some of  the
          popular  models available in the United States.  Also provided is
          general computer interfacing information.


          Serial Port Signals

          The serial port connector on your TNC is on the rear panel and is
          marked  "SERIAL."  There  are several  signals available  at this
          connector.   You  won't  need all  of  them for  standard  packet
          operation.   For some special  applications, such as  binary file
          transfer or some Bulletin  Board operations, you may want  to use
          more of them.   In that case, see TNC 2 Serial Port Pin Functions
          at the end of this chapter.

          The  pins on  the serial  port connector  of TNC  2 that  must be
          connected are shown in Table 2-1.   Note that the TNC connects to
          a computer exactly  as if the TNC were  a standard RS-232C modem.
          If you  have successfully  used  your computer  with a  telephone
          modem, hook it up to TNC 2 in the same way.  Use whatever program
          you ordinarily use to  communicate with the modem and  proceed to
          the section, Verifying Serial Port Operation.




                                          3








          Tucson Amateur Packet Radio                   TNC 2 System Manual

               Table 2-1.  Serial port signals required by TNC 2.

               Pin       Signal Name         Description

               2         Transmit Data       Serial data from your computer
                                             to the TNC.
               3         Receive Data        Serial  data  from the  TNC to
                                             your computer.
               7         Signal Ground       The  common  ground  for  both
                                             data lines.


          If your  computer is listed in  Table 2-2, refer to  the specific
          information in the following sections to connect your TNC to your
          computer.


               Table 2-2.     Computers  with  specific serial  interfacing
                              instructions.

                    Manufacturer        Model

                    Apple               Macintosh (tm)
                    Commodore           VIC-20 (tm)
                                        64 (tm)
                    IBM                 PCjr (tm)
                    Radio Shack         Color Computer (tm)
                                        Color Computer 2 (tm)
                                        Model 100
                    NEC                 8201


          Many computers require a  serial port adapter card.   These cards
          incorporate the circuitry necessary to add an RS-232C port to the
          computer.  Some popular models in  this category are the Apple II
          series, the  IBM Personal  Computer, many Radio  Shack computers,
          and the Sanyo MBC-55X series.  If you have one of these computers
          with  an "add-in" serial port, or if you have another computer we
          haven't  mentioned, you  should skip  to one  of the  sections on
          "other  computers."  If your computer has a 25-pin RS-232C serial
          port, refer to  the section Other  Computers with 25-pin  RS-232C
          Ports.   Otherwise  refer  to the  section  Other Computers  with
          Nonstandard Serial Ports.

          Some computers have no serial port and no adapter is commercially
          available.  Such computers are not suitable for use with TNC 2.





                                          4








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Apple Macintosh

          The  Macintosh serial port is  an RS-422 compatible  port, but it
          will work fine with the RS-232C serial port on your TNC. You will
          need a cable wired as shown in Fig. 2-1.


                       Macintosh (DE9P)    TNC 2 (DB-25P)

                             1 ----------------- 1
                             5 ----------------- 2
                             9 ----------------- 3
                             3 ----------------- 7
                             7 ----------------- 8
                             6 ---------------- 20

              Fig. 2-1.  Serial port wiring for Apple Macintosh.


          Note that pin 1 is not connected inside the Macintosh or the TNC.
          If you use a  shielded serial cable, which we  recommend, connect
          both pin 1s to  the shield and connect pin 1 of  the TNC 2 serial
          connector to digital ground  on the TNC circuit board.  A printed
          circuit board pad is provided for  this purpose near pin 1 of the
          serial connector.


          Commodore 64 or VIC-20

          Commodore (as well as other manufacturers such as Jameco) sells a
          voltage converter device that installs in the User port connector
          on  the rear of a VIC-20 or  Commodore 64 computer.  This adapter
          converts the internal  TTL-level voltages of the  computer to the
          proper  RS-232C  levels  and  polarities.   Unless  you  are very
          familiar  with the  inner workings of  your computer,  you should
          purchase such an adapter rather than trying to "do it yourself."


          IBM PCjr

          The  PCjr uses  standard RS-232C  voltage levels  for  its serial
          interface; however,  the connector  used is non-standard  and not
          readily  available  from  electronic   supply  dealers.    Pinout
          information for this connector is given in the IBM PCjr Technical
          Reference Manual.

          IBM  dealers sell the "IBM PCjr Adapter Cable for Serial Devices"
          for converting  the  connector  on  PCjr to  a  standard  RS-232C
          terminal connector.  This cable attaches directly between the TNC
          and the PCjr.   It is only about  3 inches long, however,  so you

                                          5








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          may  want to  obtain  a male-to-female  RS-232C extension  cable,
          which should be readily available.

          Radio Shack Color Computer

          The  Color Computer series (except for  the Micro Color Computer)
          uses  a 4-pin DIN-style connector for its serial interface.  Wire
          a cable  as shown in  Fig. 2-2 to  interface your TNC to  a Color
          Computer.   All  necessary parts  should be available  from Radio
          Shack dealers.


                        Color Computer           DB-25P

                              4 ------------------ 2
                              2 ------------------ 3
                              3 ------------------ 7

                 Fig. 2-2.  Serial port wiring for Radio Shack
                                Color Computers.


          Radio Shack Model 100 and NEC 8201

          These computers have built-in  standard RS-232C serial ports that
          are   compatible  with  the  TNC.    You  will  need  a  standard
          male-to-male RS-232C  extension cable to connect  the computer to
          the TNC.


          Other Computers with 25-pin RS-232C Ports

          If  your computer has a  25-pin RS-232C port,  you should consult
          your computer manual  or accessory  manual to see  which pins  it
          uses to  send and receive data  on, as well as which  pin is used
          for  signal   common.    Follow  the     computer  manufacturer's
          recommendations for connecting the  serial port to a modem.   You
          may also find the technical information in this section useful.

          Your TNC  is configured  as Data Communications  Equipment (DCE),
          the  technical term  for an  RS-232C modem.   Most  computers are
          configured as Data Terminal Equipment (DTE).  If this is the case
          for your computer, you will probably be able to simply wire pin 2
          of the  TNC connector to pin  2 of your  computer's RS-232C port,
          pin 3  to pin  3 and  pin  7 to  pin 7.   You  can provide  these
          connections   with   a   standard  3-   wire   male-to-female  or
          male-to-male  RS-232C extension cable,  depending on whether your
          computer has a DB25S or DB25P connector.



                                          6








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          If your  computer is configured as DCE, you will have to wire pin
          2 of  your TNC to pin 3  of the computer connector,  and pin 2 of
          the computer  connector to  pin  3 of  your TNC.   Pin  7 of  the
          computer connector will still connect to pin 7 of your TNC serial
          port.
          Some computers may require that pin 5 of the computer serial port
          connector be  connected  to an  appropriate signal.   Others  may
          require connections  for pin  8  and pin  20.   You  can use  the
          computer's output signals on pins 4 and 6 as shown in Fig. 2-3.


                            TNC 2          Computer

                               2 ------------- 2
                               3 ------------- 3
                               7 ------------- 7
                                        / ---- 4
                                        \ ---- 5
                                    /--------- 6
                                    |--------- 8
                                    \--------- 20

                Fig. 2-3.  Serial port wiring with jumpers for 
                               auxiliary signals.


          Other Computers with Nonstandard Serial Ports

          Computers with  nonstandard serial ports must  meet the following
          conditions.

          First, the signal levels  should be RS-232C compatible.   The TNC
          requires  that  the voltage  levels  sent  from the  computer  be
          greater than about +3 volts  in one state and less than  about +1
          volt in the other state.

          Second, the polarity of the signals must conform to the  RS- 232C
          standard.   This means that the low voltage state must correspond
          to a logical "1" and the high voltage state to a logical "0".

          Third,  the computer must be  able to correctly  receive a signal
          which meets the RS-232C specification.   The TNC supplies signals
          that meet this specification.

          Make or buy a cable that provides the following connections.  The
          computer serial  port common pin must  be tied to the  TNC serial
          port connector pin  7.  The  data line that  sends data from  the
          computer must be tied  to the TNC  connector pin 2.   The pin  on
          which  your computer  receives data  on must be  tied to  the TNC
          connector pin 3.

                                          7








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          If  your computer requires any other signals, you must arrange to
          provide them.  The  documentation provided with your  computer or
          its accessory serial port should clarify any special requirements
          of your port.

          Software Requirements

          Any  software package  that enables  your computer  to act  as an
          ASCII terminal  with an ordinary telephone modem should work with
          your TNC.   If you have a program that you have used successfully
          with telephone a modem and  that you are familiar with,  use that
          program to communicate with your TNC.


          Apple Macintosh

          Apple  dealers sell  a program called  MacTerm for  the Macintosh
          that works with  the TNC.  Load this program  and set the options
          according to Table 2-3.   In addition, set the TNC for  1200 baud
          as described in Verifying Serial Port Operation, below.


               Table 2-3.  MacTerm option settings for operation
                                  with TNC 2.

                      Compatibility            Terminal

                      1200 baud                VT100
                      7 bits/character         ANSI
                      even parity              UNDERLINE
                      Handshake Xon/Xoff       US
                      modem connection         80 Columns
                      "telephone" port         ON LINE
                                               AUTOREPEAT


          Commodore 64 or VIC-20

          A  BASIC  communications program  is  given  in the  Programmer's
          Reference  Guide published by Commodore.  Use the program listing
          for  "true ASCII," as these computers use a modified ASCII format
          internally.  You  will probably want to run your  TNC at 300 baud
          on the serial port with these computers.  Setting the TNC  serial
          port baud rate is discussed in the next section, Verifying Serial
          Port Operation.


          IBM PCjr



                                          8








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          The  IBM  PCjr  has a  built-in  terminal  program  in the  BASIC
          cartridge.   Start this program  by typing  TERM.  Refer  to your
          PCjr BASIC manual for details on this program.   For best results
          with PCjr,  do not run the TNC serial port faster than 1200 baud.
          Setting  the TNC serial port  baud rate is  discussed in the next
          section, Verifying Serial Port Operation.

          Radio Shack Color Computer

          There  are  several terminal  programs  available  for the  Color
          Computer.  You  will probably  want to use  a commercial  program
          (rather than writing  your own)  since the Color  Computer has  a
          "software UART" that is difficult to program in BASIC.


          Radio Shack Model 100 and NEC 8201

          These computers  have built-in terminal programs in ROM.  Consult
          your computer's documentation for instructions in their use.


          Verifying Serial Port Operation

          Turn off the power to your computer and to your TNC.  Connect the
          computer  and TNC with a  properly configured serial  cable.  Set
          the DIP switch on the rear  panel of the TNC to the  desired baud
          rate as shown  in Table 2-4.   The power  must be OFF  when these
          switches are set.

          NOTE: The serial  port baud  rate used  between the  TNC and  the
          computer  has  no relationship  to the  baud  rate used  over the
          radio.  The serial port baud rate you set on your TNC must  match
          the baud rate used by your computer serial port.


                Table 2-4.  DIP switch settings for serial port
                                  baud rates.

                    Baud Rate   Switch  1   2   3   4   5

                       300             ON  OFF OFF OFF OFF
                      1200             OFF ON  OFF OFF OFF
                      2400             OFF OFF ON  OFF OFF
                      4800             OFF OFF OFF ON  OFF
                      9600             OFF OFF OFF OFF ON

          CAUTION:  Only one of these switches may be ON at any time.

          Turn on your computer and start the terminal program.  Follow the
          directions  for the program you are using to match the computer's

                                          9








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          baud  rate  with  that selected  on  the  TNC, and  to  set other
          options.  Set your computer's port  options to 7 bits even parity
          and select either 1 or 2 stop bits.

          Turn on your TNC.  You should see a sign-on message, which should
          be  a readable  text message,  printed on  your computer  screen.
          This  demonstrates the ability  of your  computer to  accept data
          from your TNC.  If you see nothing, switch off your TNC for a few
          seconds, then  on again.   If you still see  nothing, verify your
          wiring and restart your  terminal program.  If you  see gibberish
          on your screen you should verify that you have set  the same baud
          rate for the TNC and the computer.

          When you  have successfully  read the  sign-on message from  your
          TNC, type 

               DISPLAY

          followed by  a carriage return.  You should see a lengthy list of
          items  on your screen.  This verifies  the ability of your TNC to
          accept and respond to input from your computer.

          Your  serial interface  is now  working.   If you  are completing
          construction  of your  TNC,  return to  the  assembly manual  and
          continue from where you were directed to this manual.


          TNC 2 Serial Port Pin Functions

          This  section describes the pins used on the TNC's RS-232C serial
          port connector.  It is intended for packet operators with special
          applications  requiring hardware  handshaking.   This information
          should not be needed by most users.


                      Table 2-5.  RS-232C Pin Designations

                   Pin     Mnemonic         Name

                    1         FG        Frame Ground
                    2         TXD       Transmit Data
                    3         RXD       Receive Data
                    5         CTS       Clear To Send
                    6         DSR       Data Set Ready
                    7         SG        Signal Ground
                    8         DCD       Data Carrier Detect
                    9         ---       + 12V unregulated reference
                   10         ---       - 12V unregulated reference
                   20         DTR       Data Terminal Ready


                                          10








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Frame Ground is provided for attachment to the chassis of the TNC
          and the chassis  of the attached  device (computer or  terminal).
          This pin  is brought out to a  feedthrough on the TNC  2 PC board
          near pin  1 of  the  serial connector.   It  is not  electrically
          connected anywhere else on the TNC circuit board.

          Transmit Data is an input  line to the TNC on which  the attached
          device sends data.

          Receive Data is an output line from the TNC on which the attached
          device receives data.

          Clear To  Send is an output  from the TNC signaling  the attached
          device to send  or refrain from  sending data to  the TNC.   This
          line is used for hardware flow control.

          Data Set  Ready is  an output from  the TNC telling  the attached
          device that the TNC is operational.

          Signal  Ground is  the common,  or return,  path for  all signals
          between the TNC and the attached device.

          Data  Carrier Detect  is an  output from  the TNC.    As normally
          configured, DCD reflects  the status of the CON LED:   It is true
          when an  AX.25  connection exists  between your  TNC and  another
          station;   it  is   false   when  no   connection  exists.   This
          configuration is useful  when the  TNC is used  with a  telephone
          style Bulletin  Board system, since the  AX.25 connection, analo-
          gous to a modem  signal on the telephone, indicates  the presence
          of  a user.  Shorting JMP1 on the  TNC 2 PC board will cause this
          output to always be true.

          Pins 9  and 10 provide access to the TNC's unregulated +/-12 volt
          supplies  for use by an external device.   These are not intended
          to  power an accessory, and should not  be used to source or sink
          more than a couple of milliamperes!















                                          11








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 3  RADIO INTERFACING




          Computer interfacing,  covered in  the previous chapter,  is only
          half the interfacing task.  The other half is connecting your TNC
          to a radio.

          Before you interface the  TNC to your radio you  should calibrate
          your modem frequencies.  If you have just assembled your TNC, you
          should have done  this as  part of the  assembly procedure.   The
          complete modem calibration procedure is described in Chapter 5.

          Interfacing  the  TNC  to  your  radio  involves  connecting  the
          following signals at J2.

          Pin 1  Microphone audio, from the TNC to your transmitter.

          Pin 2  Ground, audio and PTT common.

          Pin 3  Push-to-talk, to allow the TNC to key your transmitter.

          Pin 4  Receive audio, from your receiver to the TNC.

          Pin  5   Squelch  input  (optional) to  allow  the TNC  to detect
          activity on a shared-mode channel.


          This chapter describes how to connect these signals  between your
          TNC and  your radio and  how to adjust  the receive  and transmit
          audio  levels  appropriately.    The  interconnection  should  be
          planned so as  to minimize pickup of stray audio  and RF noise by
          the lines.  If  possible, you should set  up your packet  station
          with a  monitor speaker and be  able to operate on  voice without
          disconnecting the TNC.

          This chapter assumes that  you are using an FM radio.  If you are
          operating on another mode,  such as SSB, most of  the information
          is still applicable.

          Two interfacing methods are presented.  You will have  to use the
          second  method if you can't adjust the audio levels properly with
          the first method.   They  require no special  test equipment  for
          adjusting the audio levels.   If FM test equipment  is available,
          however, it  should be used as described.  You will need a second
          receiver in your  shack that you  can use to  listen to your  own
          signal.   Read  the  remainder of  this chapter  carefully before
          starting to interface your TNC to your radio.


                                          12








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Method 1:  Direct Connection to Microphone and Speaker

          TNC 2 was designed to allow hookup and initial testing to be done
          without  any  modifications to  the  radio  or  any signal  level
          balancing devices in the cables.

          For  Method 1,  the TNC's  audio will  be fed  directly into  the
          microphone connector  or similarly connected auxiliary  jack, and
          the  output  of  the  TNC  will  be  adjusted  to give  a  proper
          modulation  level.   The  receiver audio  will  be taken  from an
          earphone plug or speaker jack and fed directly to the TNC.

          This  method  is expedient  but,  unless  you  have an  auxiliary
          speaker/mike jack, it doesn't allow you to monitor the channel or
          to conveniently use the rig on voice.  The connection may also be
          susceptible  to RFI  from  nearby Amateur  and commercial  trans-
          mitters.   For  these reasons  you  may want  to  use the  second
          interface method for your  permanent station interface, after the
          initial testing phase.

          Connect your TNC to your radio. Turn on your TNC and computer and
          start your terminal program.   Connect the radio to a  dummy load
          and listen to the transmission with another nearby radio.

           1.  Enter the modem calibration procedure by typing

                    CALIBRA

          and  a carriage return.  Press the K  key on your keyboard to key
          the transmitter, then tap  the space bar until the higher  of the
          two tones  is heard.   Pressing the  K key again  will unkey  the
          transmitter.   After  the transmitter  has been  keyed for  a few
          seconds,  it  will be  shut  off  automatically by  the  transmit
          watch-dog  circuit.  As  you perform  the adjustments  below, you
          will have to  periodically unkey then  re-key the transmitter  by
          typing the  K key.   If you wish  to defeat the  watch-dog timer,
          place JMP4.

           2.  With  the TNC  keying the transmitter  and transmitting  the
          higher  of  the two  tones, adjust  the  transmit audio  level as
          follows.   With a small screwdriver, adjust trimpot R76 while you
          listen  to the monitoring receiver.  Turn the adjustment screw on
          R76 clockwise (CW) until no increase in output level is heard  at
          the monitoring receiver.

           3.   Rotate the adjustment  screw of R76  counterclockwise until
          the  audio  signal on  the monitoring  receiver is  slightly, but
          noticeably, reduced from the maximum level.



                                          13








          Tucson Amateur Packet Radio                   TNC 2 System Manual

           4.  Press the K key to return to receive mode and type Q to exit
          the calibration routine.  Be sure to remove JMP4 if you placed it
          to defeat the watch-dog timer.  You have now set your transmitter
          deviation to approximately the correct level.

           5.  With  your radio in the receive mode,  open the squelch con-
          trol so that  a steady hiss would be heard on a speaker.  Set the
          volume control so the  DCD LED on your TNC  flickers occasionally
          with  no received signal.  This is approximately the proper level
          for best receive performance from your TNC's modem.

          If  you notice a significant hum level  in the monitored audio in
          Step 3,  take measures to remove  it.  This may  require shielded
          wire (recommended in any event) in your microphone audio circuit.
          If your  transmitter has  an adjustable microphone  gain control,
          try  reducing  the  sensitivity  of  the  transmitter  microphone
          circuit and increasing the signal level from your TNC to minimize
          hum or other noise problems.


          Method 2:  Accessory Jack or Interface Box Connection

          If your radio has an accessory jack with PTT, transmit audio, and
          receive audio  signals, the  interface can  be done  through this
          jack  with  the addition  of only  a  single resistor  inside the
          radio.  This  resistor should be  placed in series  with the  TNC
          audio output where  it is  connected to the  microphone audio  to
          provide isolation.  The method  of determining the value required
          will depend on the radio used, and is described below..

          If your  radio does not have an accessory jack and you don't wish
          to add a connector to your radio, you should construct a separate
          external  interface  box.    This box  will  permit  simultaneous
          connection  of  your  TNC and  a  microphone.    Again, a  series
          resistor  should be placed in  series with the  TNC audio output.
          It  will either have  its own speaker or  pass the speaker signal
          through to a connector so that you can monitor the  receive audio
          while your TNC is hooked up.  

          Regardless  of whether you use  an accessory jack  or an external
          interface   box,   you  should   use   shielded   wire  for   all
          signal-carrying leads.   The connector types and  pinouts will be
          determined by the connector jacks on your radio.

          When  all  required cables  have been  assembled  and the  TNC is
          connected to the radio, you are ready to set the levels according
          to the following procedure.

           1.  Remove the  shunt attenuator element, R57 in  the microphone
          audio section of your TNC.

                                          14








          Tucson Amateur Packet Radio                   TNC 2 System Manual

           2.   Temporarily solder a variable resistor  in place of R(S) in
          Fig. 3-3 or Fig. 3-4.  The maximum value of this resistor must be
          determined by experiment, but 500K should handle most cases.

           3.   Connect your TNC to  the radio.  Connect  the microphone to
          the radio, or to the interface box if one is being used.  Connect
          the radio to a dummy load.

           4.   Turn  on  your TNC  and  computer and  start your  terminal
          program.  Enter the modem calibration procedure by typing

                    CALIBRA

          Press the  K key to key  the transmitter, then tap  the space bar
          until the higher of  the two tones is heard.   Pressing the K key
          again will unkey the transmitter.  After the transmitter has been
          keyed for a few seconds, it will be shut off automatically by the
          transmit watch-dog circuit.   As you perform the adjustments  be-
          low,  you  will  have  to  periodically  unkey  then  re-key  the
          transmitter  by typing  the K  key.   If you  wish to  defeat the
          watch-dog timer, place JMP4.

           5.  With  the TNC  keying the transmitter  and transmitting  the
          higher  of  the two  tones, adjust  the  transmit audio  level as
          follows.   With a small  screwdriver, adjust trimpot  R76 and set
          the output of  your TNC to  about 70% of its  maximum undistorted
          value  as observed  on  an oscilloscope  monitoring the  transmit
          audio   at  JMP7.    This  level  may  be  estimated  without  an
          oscilloscope by turning R76 clockwise to  maximum (indicated by a
          clicking sound inside the trimmer) and then backing off 15 turns.
          At this  point the signal  amplitude at JMP7 should  be about 2.5
          volts peak-to-peak.

           6.  Adjust the  variable resistor installed in step 2 for proper
          modulation level (typically between 3.0 and 4.5 kHz deviation for
          Amateur FM).  If FM test equipment is  not available, adjust R(S)
          as  described in  steps 2  and 3  of Method  1 above,  using R(S)
          instead of R76.

           7.  Press the K key to return to receive mode and type Q to exit
          the  calibration  routine.   You  have now  set  your transmitter
          deviation to approximately the correct level.  Remove JMP4 if you
          placed it in Step 4.

           8.   Carefully  remove  the variable  resistor  and measure  its
          value.   This is  the proper  value of  R(S) for  your particular
          radio.




                                          15








          Tucson Amateur Packet Radio                   TNC 2 System Manual

           9.  Select the  nearest standard value fixed resistor  (1/4 watt
          is fine) and  permanently install  this resistor as  R(S) in  the
          interface circuit.

          10.  If you have  access to FM test equipment, check  to see that
          the modulation level  is still within the limits of  3 to 4.5 kHz
          deviation.   If it is not,  make a final adjustment  with the TNC
          transmit audio level control, R76.

          11.  Open the squelch control on your radio so that a steady hiss
          is heard.   Set  the volume control  so the  DCD LED on  your TNC
          flickers  occasionally.  This is approximately  the  proper level
          for best receive performance from your TNC's modem.






































                                          16








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 4  OPERATION I:  GETTING STARTED




          This  chapter will guide you  through the basics  of packet radio
          operation with TNC 2.  Packet radio has a great deal of power and
          flexibility, and this chapter only scratches the surface of  your
          packet station's  capabilities.   However, it contains  the basic
          information required to  get you on the air  with packet radio to
          begin exploring this new mode. 

          First Steps

          The serial port baud rate switches  on the back of the TNC should
          be set  to the same baud  rate as your computer.   These settings
          are  described in  Chapter  2,  Computer  Interfacing.   Set  the
          following switches, with  the TNC OFF (be sure only  one of these
          switches is ON when the TNC is powered up):


                 Table 4-1.  DIP switch settings for 1200 baud
                                radio data rate.

                               Switch    Setting

                                  6        OFF
                                  7        ON
                                  8        OFF


          This sets a radio baud rate of 1200 baud.  The radio baud rate is
          not related to the computer baud rate.

          Turn on  your TNC.  You  should see something like  the following
          display.

                    Tucson Amateur Packet Radio TNC 2
                    AX.25 Level 2 Version 2.0
                    Release nn
                    Checksum $xx
                    cmd:

          The  first five  lines are  the sign-on  message, which  you will
          normally see only  when you power up the TNC.   (See the Software
          Release Notes  for values of nn and xx.)  The Command Mode prompt
          cmd: will appear when the TNC is in Command Mode  and is ready to
          accept your instructions.



                                          17








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          You  may see  some anomalies  in the  appearance of  the display,
          which  will be corrected as you proceed through the next section.
          The sign-on  message may appear double-spaced,  or characters you
          type  may be  displayed  twice.   You  may even  see  incorrectly
          displayed characters.


          Entering Commands

          In the examples in  this chapter, text  that you are supposed  to
          type will appear in boldface.  Text typed by the  TNC will appear
          in normal type:

                    cmd:RESET

          This  means  that you  are supposed  to  type the  text, "RESET",
          following the Command Mode prompt which  the TNC typed.  End  the
          line with a carriage return.  All command entries will end with a
          carriage return, abbreviated  <CR>.   The <CR>  at the  end of  a
          command normally won't be mentioned.

          You should see the TNC's response to the RESET command:

                    bbRAM loaded with defaults

                    Tucson Amateur Packet Radio TNC 2
                    AX.25 Level 2 Version 2.0
                    Release nn
                    Checksum $xx
                    cmd:

          The TNC has reloaded all user-settable parameters normally stored
          in the battery backed-up RAM (bbRAM).  All parameters are now set
          to  their default values.  The TNC has also re-initialized itself
          exactly as it would  upon power-up, and typed a  sign-on message.
          You  probably won't  use  this  command  often.    The  TNC  will
          automatically reload  the bbRAM at power up  if it finds that the
          data is bad.

          If you make mistakes while entering  commands to the TNC, you can
          make corrections.  To erase the last character you typed, enter a
          <BACKSPACE>  character.    The  TNC  will  throw  away  the  last
          character you typed  (unless you are at the  beginning of a line)
          and try to erase the  character from your screen.   Input editing
          will be discussed in  more detail in the section,  "Special Input
          Characters."

          You are now  ready to start  setting up the  parameters you  will
          use.  You may be satisfied with most of the defaults for now, but
          a few parameters will have to be changed!

                                          18








          Tucson Amateur Packet Radio                   TNC 2 System Manual

                    cmd:MYCALL WA7QST
                    was       NOCALL
                    cmd:

          Type  the  text,  "MYCALL  WA7QST", following  the  command  mode
          prompt.  Of  course, you should substitute your own call sign for
          WA7QST.  Don't forget the <CR> at the end of the line.  Your call
          sign will be used by the TNC as its "address."   The TNC responds
          by  telling you the previous  value of the  MYCALL parameter, and
          gives you a new Command Mode prompt.

          Now try typing just the command by itself:

                    cmd:MYCALL
                    MYCALL    WA7QST

          You can see  the current value of  most parameters by  typing the
          command that  sets the parameter followed  by just a <CR>.   This
          verifies that the TNC accepted your call sign.

          The next section describes the commands you will use to configure
          the TNC  for proper  text display for  your particular  computer.
          You  may not use these commands again unless you change computers
          or terminal programs.   The following sections, "Basic Operation"
          and "Monitoring Channel Activity," describe the commands you will
          use for your everyday packet operations.  With these commands you
          will be ready for the section, "Your First Packet QSO."  The last
          section  of  the  chapter,  "Special  Input  Characters" contains
          information on input editing and other special characters used by
          the TNC.

          If  you  intend   to  use  your  packet  station  for  "advanced"
          applications, such  as a computer  Bulletin Board or  binary file
          transfers,  you should  continue  with Chapter  5, Operation  II:
          Further Details.  However, Chapter 4 contains all the information
          that   is  needed  for  most  packet  operations.    For  a  full
          description of  all commands, refer  to the appropriate  entry in
          Chapter 6, TAPR TNC 2 Commands.

          Most commands  can be abbreviated, and  the minimum abbreviations
          for each command are given in the listings in Chapter 6.  For the
          sake of  clarity, only the  full command names  are used  in this
          chapter.


          Serial Port Configuration

          This section  describes the commands you will  use to set up your
          TNC to work best with your computer.


                                          19








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Parity and Word Length

          If  messages  from  your  TNC appear  garbled,  with  incorrectly
          displayed characters,  you may  need to change  the TNC's  serial
          port parity  and word length.   (We assume that you  have set the
          baud rate correctly.  See Chapter 2 if the baud rate needs to  be
          changed.)   The most  common parity and  word length combinations
          are 7 bits,  even parity  (the TNC  default), and  7 bits,  space
          parity.   The TNC default will  probably be accepted even if your
          computer  actually uses  the latter  setting.   If your  computer
          receives 8 bits as data, you may have to set  space parity, since
          text may  otherwise be interpreted  as graphics or  other special
          characters.    To set  7 bits,  space  parity, use  the following
          combination:

                    AWLEN 8        (8-bit words)
                    PARITY 0       (no parity bit)

          To return to 7 bits, even parity, set

                    AWLEN 7        (7-bit words)
                    PARITY 3       (even parity)

          One of these combinations  will satisfy most computers.   You are
          more likely to require a different setting if you have a terminal
          rather than a computer,  or if you have configured  your terminal
          port for some special application.

          If your  computer requires  odd parity,  set PARITY  1.   If your
          computer detects framing errors, try setting

                    AWLEN 7        (7-bit words)
                    PARITY 0       (no parity bit)

          for shorter characters.  For longer characters, set:

                    AWLEN 8        (8-bit words)
                    PARITY 1 or PARITY 3


          Echos

          You may see two characters on your screen for every character you
          type, for example:

                    cmd:RREESSEETT

          Your computer is echoing the characters you type, and the  TNC is
          also echoing them.  In this case,  set ECHO OFF to stop the TNC's
          echos.   If you later use your  TNC with a different computer, or

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          with a different terminal program,  you may see nothing displayed
          when you type.  In that case, set ECHO ON.


          New Lines and Line Wrapping

          If  everything  displayed  appears  to  be  double-spaced,   your
          computer is adding an extra linefeed (<LF>) whenever it  displays
          a carriage  return (<CR>).  Set  AUTOLF OFF to keep  the TNC from
          also adding an <LF>.  If you change equipment you may have to set
          AUTOLF ON to restore the TNC's automatic linefeeds.

          The screen-width parameter is set by  default to 80, the width of
          many CRT displays.  The TNC will send an extra <CR> (or <CR> <LF>
          if  AUTOLF is  ON) when 80  characters have  been displayed  on a
          line.   If your computer does not automatically break long lines,
          you will  need to  set  the screen  width to  the  width of  your
          display.   For  example, for  a  computer using  a TV  set for  a
          display,  you  would set   SCREENLN  40.   If your  computer does
          automatically  break  long lines,  you should  set SCREENLN  0 to
          disable  this feature on  the TNC.   Otherwise, you will  get two
          <CR>s when the line wraps around.

          A  few computers will frequently  lose the first  characters of a
          line  when  several  lines  are typed  in  rapid  succession, for
          example, in the sign-on message.  You can give the  computer more
          time between lines by setting NUCR ON (delay after <CR>), or NULF
          ON (delay  after <LF>).   The delay  is adjusted by  NULLS, which
          sets a number of character-times for the delay.


          Basic Operation

          You  can learn  quite a  bit about  your TNC's  operation without
          actually transmitting anything.  For your first experiments, your
          TNC  will be "talking to itself," allowing you to become familiar
          with it before you go on the air.

          Disconnect  your  radio  from your  TNC  and  turn  off the  TNC.
          Install  the digital loopback jumper, JMP10.  The analog loopback
          jumper,  JMP7, should not be installed.  Connect your computer to
          the TNC with  your serial cable.  Turn on  the computer and start
          your terminal program.


          A Connecting and Disconnecting Exercise





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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Packet radio QSOs are started by a connect process, which sets up
          the   "handshaking"  between   the  two  stations   that  insures
          error-free communications.   QSOs are terminated  by a disconnect
          process, which  leaves  both stations  free  to start  new  QSOs.
          Packet QSOs  can  also  make use  of  digipeaters,  other  packet
          stations which  can automatically relay packets  from one station
          to the other over a specified route.
          To  see how this works, you can  have your TNC connect to itself.
          Since you  have set the  TNC up  for digital  loop-back, it  will
          receive all packets that it sends.  Try the following:

                    cmd:CONNECT WA7QST
                    *** CONNECTED to WA7QST

          replacing  WA7QST with  your own  call sign.   The  TNC generates
          packets initiating  and confirming  the connection.   The packets
          aren't actually  converted to audio signals  and transmitted over
          the radio, but  they are otherwise just like packets  you will be
          transmitting later on.

          The  *** CONNECTED to message  tells you that  the connection was
          successful.  You should also  notice that the CON LED has  lit up
          and that you do not see a new cmd:  prompt on the next line.  You
          are now in Converse Mode, ready to start talking.  Try it.   Type
          your message, ending the line with a <CR>.

                    Hello, there.
                    Hello, there.

          The  <CR>  causes  your message  to  be  put  into  a packet,  or
          "packetized," and transmitted.   (We explain in the  next chapter
          how you  can use  a different character  to send  packets.)   The
          underlined text  is a message that  the TNC received  in a packet
          and  displayed.  Whenever you  are in Converse  Mode anything you
          type will be assembled into a packet addressed to the station you
          are talking  to  and transmitted.   If  there isn't  a QSO  (con-
          nection) in progress, the packet will be sent to the address CQ.

          In  the example  above,  your TNC  entered Converse  Mode automa-
          tically after the  connect took place.  You can  also command the
          TNC  to move  back and  forth between  Command Mode  and Converse
          Mode.

          To  return to Command Mode,  you must enter  a special character,
          Control-C (abbreviated  <CTRL-C>), or  else send a  BREAK signal.
          "Control"  characters  are  usually  entered by  holding  down  a
          special control key and then typing another key without releasing
          the control key.  If your keyboard doesn't have a key marked CTRL
          or something similar, consult the documentation for your computer
          or terminal program  to see how to  enter control characters.   A

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          BREAK signal is  a special transmission (not  an ASCII character)
          which your computer may be able to produce.

               NOTE:   If <CTRL-C> will cause your computer to do something
          to interfere with packet operations, such as halting the terminal
          program,  and  you can't  send BREAK  signals,  you will  have to
          change the character  that returns you to Command Mode.   See the
          section on "Special Input Characters," below.

          Now type  a <CTRL-C>.  The TNC doesn't echo the <CTRL-C>, but you
          should  immediately  see a  Command Mode  prompt.   To  return to
          Converse Mode, enter the command CONVERS:

                    <CTRL-C>
                    cmd:CONVERS
                    Whatever I type in Converse Mode is transmitted.
                    Whatever I type in Converse Mode is transmitted.
                    <CTRL-C>
                    cmd:

          To terminate  the QSO,  you must end  the connect  by giving  the
          DISCONNE  command.  The TNC will transmit packets terminating the
          conversation and notify you when the disconnect is complete:

                    cmd:DISCONNE
                    *** DISCONNECTED

          An  actual QSO  might  be terminated  by  the other  station,  of
          course.  In that case, you would see the *** DISCONNECTED message
          without having issued the command.

          You have just performed  the basic operations of any  packet QSO.
          You established  a connection with  the desired station  to begin
          the QSO, sent and received  some messages, and disconnected  from
          the station at the end of the QSO.


          Digipeating

          You may  wish to have a  QSO with another packet  station that is
          beyond your direct radio range.  If a third packet  station is on
          the air and both you and the  station you want to talk to are  in
          range of this third station, that station can relay your packets.
          You set up the  packet routing when you initiate  the connection.
          Your TNC will then  automatically include the routing information
          in the packets it sends.

          The diagram below shows an example situation in which digipeating
          is useful.


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                                    AD7I
                                   /    \
                    N2WX _________/      \_________ WA7QST

          You are  station WA7QST, and you  want to have a  packet QSO with
          N2WX.  There is a mountain in the way and you are not  in simplex
          range of each other.   However there is a station located  on the
          ridge, AD7I, which is in range of both you and N2WX.

          You direct the TNC  to set up a connection to  N2WX using AD7I as
          an intermediate digipeater as follows:

                    cmd:CONNECT N2WX VIA AD7I

          You  can specify  a  routing list  of  up to  eight  intermediate
          stations.   For example,  consider a modification  of the example
          above:

                                    ____
                                   /    \
                    N2WX _________/      \_________ WA7QST
                         .                        .
                             .                .
                               KV7D . . . NK6K

          AD7I  has turned  off his station,  but you  can contact  N2WX by
          going around the mountain  through NK6K and KV7D.   This time you
          issue the connect command like this:

                    cmd:CONNECT N2WX VIA NK6K, KV7D

          You specify the digipeaters in the order you would encounter them
          going  from your  station to  the station  to  which you  wish to
          connect.

          Your station can  also act  as a digipeater  for other  stations.
          This doesn't require any special actions on your part -- your TNC
          will   do  everything   automatically.     If  your   station  is
          digipeating, you  may occasionally notice your transmitter keying
          during lulls in your own conversations.


          Unsuccessful Connections

          Sometimes you  will initiate  a connect  sequence  that can't  be
          completed.   The station may not be on the  air, or it may not be
          within  range of your  station.  You may  have even mis-typed the
          other call sign.  If the TNC does not get a response to its first
          connect packet, it will try again.  You can control the number of
          attempts the TNC will make with  the command RETRY.  The  default

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          number of retry attempts is 10.  If the TNC doesn't get an answer
          after this number of  transmissions, it will give up  and display
          the message

                    *** retry count exceeded
                    *** DISCONNECTED

          The  retry count  is also used  once the  QSO has  started.  Each
          transmission  sent to  the  other station  is "acknowledged,"  or
          ACKed by the other station,  and vice versa.  The ACK  means that
          the  packet was received and that the CRC checksum indicated that
          it  was received  without errors.   This  is the  means  by which
          packet radio  can ensure error-free communications.   Sometimes a
          packet  won't be received correctly  by the other station, either
          because of accidental interference from another packet station (a
          collision),  or  because of  other channel  noise.   If  your TNC
          doesn't get an  ACK soon  enough, it retransmits  the packet  and
          increments  the retry  count.    If the  count  set  by RETRY  is
          exceeded, the  TNC will automatically disconnect  and display the
          same message:

                    *** retry count exceeded
                    *** DISCONNECTED

          The automatic  disconnect feature  keeps a TNC  from indefinitely
          retransmitting a  packet and tying up the  channel under hopeless
          conditions.   For example, an intermediate  digipeater might have
          been shut down,  or the RF channel might have deteriorated to the
          point  of being  unusable.   The other  operator might  have even
          turned  off  his  station  without  disconnecting.    If you  are
          operating  under  special  conditions,  such  as  a  marginal  HF
          channel, you can set RETRY 0 to disable all automatic disconnects
          (the retry limit is never reached).


          Monitoring Channel Activity

          In  addition  to displaying  messages  from the  station  you are
          connected  to, your  TNC can  allow you  to monitor  other packet
          activity on the  channel.   You can "read  the mail,"  displaying
          packets between other stations.  Your TNC will also keep track of
          stations heard during a session.  This section will describe some
          of the monitor functions.

          Monitoring  is enabled or disabled  by the MONITOR  command.  You
          can try  this out in  digital loop-back mode  while disconnected.
          Type:

                    cmd:MONITOR ON


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                    cmd:CONVERS
                    This is a test packet.
                    WA7QST>CQ:This is a test packet.

          Since you aren't  connected to another  station your packets  are
          sent to the address "CQ," i.e.,  anyone.  The packet you sent was
          "heard"  by the TNC and displayed, along with the sending station
          and the destination.

          If  you also  want to  see any  intermediate digipeater  stations
          being used, you can set MRPT ON.  This feature would be useful if
          you later  want  to  connect  to  one of  the  stations  you  are
          monitoring and will need a digipeater route in order to reach it.
          For example, you might see the following display:

                    WB6YMH>WD0ETZ,KV7B:Hello, Bill!

          This packet was sent from WB6YMH via KV7B to WD0ETZ.

          If there are  several digipeaters,  or if the  message lines  are
          long, the  display may  be difficult  to read.   You can  put the
          address  header on  a  separate line  from  the text  by  setting
          HEADERLN ON:

                    WB6YMH>WD0ETZ,KV7B:
                    Hello, Bill!

          Ordinarily, your  TNC will  stop displaying monitored  packets if
          you  connect  to  another  station, permitting  you  to  converse
          without  interruption.   If  you want  to monitor  activity while
          connected to a packet station, set MCON ON.

          To display a list of stations  heard since the last time your TNC
          was powered up, type

                    cmd:MHEARD
                    AD7I
                    WA7GXD
                    N2WX
                    NK6K
                    KV7B*

          The  last several stations whose  packets were heard  by your TNC
          are  displayed.   The  entry "KV7B*"  means  that KV7B  was heard
          digipeating a packet rather than sending one of his own.  You can
          clear the "heard log" with the command MHCLEAR.


          You  can see  the settings  of  the monitor  parameters described
          above, as well as several others, by typing DISPLAY MONITOR.

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          Tucson Amateur Packet Radio                   TNC 2 System Manual


          Your First Packet QSO

          Although  there  are still  a number  of  features you  should be
          familiar with for comfortable  packet operation, you are probably
          eager to get on  the air and try out  your TNC.  Arrange  to have
          another packet operator  get on the air to help  you get started.
          Make sure that your  friend will be close enough to  ensure solid
          copy, with  no FM "popcorn" noise.   It's best if you  can get an
          experienced packet operator to help you get started.  If you  are
          both beginners,  try to have both  stations in the  same room and
          operate on low power or into dummy loads.



          Starting the QSO

          You are ready to initiate a connect.  For the sake of example, we
          will continue  to use WA7QST in  place of your call  sign, and we
          will use WB0QRP  for your friend's  call.  Make  sure you are  in
          Command Mode, and type

                    cmd:CONNECT WB0QRP

          After a moment you should see the message

                    *** CONNECTED to WB0QRP

          and  you will  be in  Converse Mode.   Your  friend will  see the
          message

                    *** CONNECTED to WA7QST

          and he will also be in Converse Mode.  You  have begun your first
          QSO.

          If you have  trouble connecting, make sure  your microphone drive
          level  is set  properly, as described  in Chapter  3.   It may be
          helpful to  have an experienced  packet operator  listen to  your
          transmissions and  monitor with his  TNC.   You can also  try the
          following procedure.  Both you and your friend should set MONITOR
          ON,  enter Converse  Mode and  send some  packets.   Each station
          should display packets sent by the other.  If only one station is
          "hearing"  properly, you  can  concentrate on  the modulator  and
          transmitter of that station  and the demodulator and receiver  of
          the  other station.  You  can try experimenting  with the TXDELAY
          timing parameter for the sending TNC.  Set TXDELAY 64  for a long
          delay.   If  this solves  the problem,  you can  back off  to the
          smallest value that works consistently.


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Exchange several  messages to get a  feel for this new  mode.  If
          you  monitor  the radio  transmit  indicators and  listen  to the
          speaker audio from  the two rigs, you will have  a better idea of
          what is  happening.  You radio will be inactive most of the time,
          even while you are actually typing.  When you get to the end of a
          line and type  a <CR>, your radio will be  keyed briefly and your
          friend will hear a "brrrraaaap" on  his speaker.  As your message
          is displayed on his computer, his radio will be keyed for an even
          shorter time and you will hear  a "brraap" on your speaker.  This
          is the ACK, or packet acknowledgment coming back.  Your TNC takes
          note  that  the packet  was  received correctly,  but  nothing is
          displayed on your screen.


          Digipeating

          Now  that you are on the air, you and your friend can try out the
          TNC's   digipeating  capabilities.     This   is   actually  more
          interesting if  you have  at least three  stations participating,
          but you can get the feel for it with two stations.

          Return to Command Mode and disconnect from the other station:

                    <CTRL-C>
                    cmd:DISCONNE
                    *** DISCONNECTED

          Now issue the following command.

                    cmd:CONNECT WA7QST VIA WB0QRP

          As before, substitute your call for WA7QST and your friend's call
          for WB0QRP.  You are requesting a connect to yourself, as you did
          before  in digital loop-back mode, but this  time you are using a
          sort of RF loop-back.  You transmit packets to your friend's TNC,
          which   relays  them  back  to  you.    When  the  connection  is
          established you will see

                    *** CONNECTED to WA7QST VIA WB0QRP

          and you will be in Converse Mode.  Your friend won't see anything
          displayed on his computer  and his TNC's state won't  be affected
          at  all  by your  QSO.   In fact,  your  friend could  issue this
          connect request,

                    cmd:CONNECT WB0QRP VIA WA7QST

          and  you  can  carry  on two  separate  conversations  completely
          independently.  Monitor the  radio transmit indicators and listen


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          to  the speaker audio.  See if you can follow the packets and the
          acknowledgments back and forth.

          Monitoring on the Air

          This is  a good  time to  try out  the  TNC's monitor  functions.
          While you and your friend are separately connected, type

               <CTRL-C>
               cmd:MONITOR ON
               cmd:MCON ON
               cmd:CONVERS

          You  will  be  able to  see  both  your  "conversation" and  your
          friend's conversation.  Also try HEADERLN ON and MHEARD.


          Special Input Characters

          The TNC  has a number of  special characters that can  be used to
          control its actions.   Many  of these special  characters can  be
          used  to "edit"  commands and  packet text  as they  are entered.
          These features can all  be customized to suit you and your compu-
          ter.  Most  of the special input characters we  will describe are
          active  in both Command  Mode and  Converse Mode;  the exceptions
          will be noted.

          The character used to  return to Command Mode from  Converse Mode
          is by default  a <CTRL-C>.  (Sending a BREAK  signal also works.)
          This   character  does  nothing  in  Command   Mode,  so  if  you
          accidentally  enter it twice you  won't mess up  the next command
          line.  You  can change the Command Mode  entry character with the
          command  COMMAND.   This  is one  of  several commands  that  set
          special  character functions.   You can choose  any character for
          this  function, by entering the ASCII character code for the key.
          For  example, you can  use a  <CTRL-E> to  enter Command  Mode by
          setting

                    cmd:COMMAND 5
                    was       $03

          The TNC  displays the previous  value in  hex, and  you can  also
          enter character codes in hex  if you prefer.  All of  the special
          characters  described below  can be  changed in  the same  way as
          COMMAND.

          We have already mentioned that you can erase mis-typed characters
          by  typing  the  <BACKSPACE>  character.    You  can change  this
          character with the command DELETE.  If you set DELETE ON, you can
          erase characters by typing the <DELETE> character; setting DELETE

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          OFF returns to using  <BACKSPACE>.  You will probably want to use
          the  same key  that  your  computer  normally  uses  to  rub  out
          characters.   <BACKSPACE> is more commonly  used than <DELETE> by
          personal computers.  If  you aren't sure whether your  rubout key
          produces  <DELETE> or  <BACKSPACE> characters,  you can  try both
          settings of the DELETE command and see which works.

          When you rub out  a mis-typed character, the TNC will  attempt to
          correct the screen display.  This will work for most computers as
          well as display-type terminals.   It won't work for hardcopy-type
          terminals  or possibly  with a  few computers.   If  your display
          doesn't look right  after you  rub out a  character, try  setting
          BKONDEL  OFF.  The  TNC will not  try to correct  the display but
          will indicate the rubout with a "\" character (<BACKSLASH>).  You
          can restore display correction by setting BKONDEL ON.

          If you make  several mistakes in  a line, or  if you change  your
          mind, you may  want to cancel the whole line  rather than rubbing
          out the  characters one at  a time.   You can cancel  the line by
          typing  <CTRL-X>.  The TNC will display a <BACKSLASH> followed by
          <CR>.  If you are in Command Mode, you will see a new prompt:

                    cmd:Hi, John, how are you?<CTRL-X>\
               [You started typing text while in Command Mode.]
                    cmd:CONVERSE
                    Hi, John, how are you?

          The cancel-line character  can be changed to  any ASCII character
          by the command CANLINE.

          If  you have  changed  your input  by  rubbing out  and  retyping
          characters,  you may want  to see a  "fresh" copy of  your input,
          especially if you have set BKONDEL  OFF.  The TNC will retype the
          line you are entering when you type <CTRL-R>:

                    cmd:CONNECT KB7\\\WA7<CTRL-R>\
               [You mis-typed the call sign.]
                    cmd:CONNECT WA7GXD

          Here  the user mis-typed the  first three characters  of the call
          sign  and  rubbed them  out.    The TNC  displayed  "\"  for each
          character  rubbed out.    The user  then  retyped the  characters
          correctly  and redisplayed the line.  He finished typing the call
          sign  on the  new  line.   The  redisplay-line character  can  be
          changed to any ASCII character by the command REDISPLA.

          If  your TNC  displays information  faster than  you can  read it
          before it scrolls  off the screen,  you can halt  the display  by
          typing <CTRL-S>.  To resume output from the TNC to your computer,


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          enter <CTRL-Q>.   These characters  can be changed  to any  ASCII
          character by the commands STOP and START, respectively.

          You may occasionally  want to  include one of  the special  input
          characters  in a packet.   For example, to  send several lines at
          once in  the same packet, you  would have to include  <CR> in the
          packet at  the  end of  each  line, bypassing  its  "send-packet"
          function except at the actual end of the packet.  You can include
          any  character in  a packet  including all special  characters by
          prefixing it with the pass character, <CTRL-V>.  For example,

                    I wasn't at the meeting.<CTRL-V><CR>
                    What happened?

          Ordinarily,  this message  would  be sent  as  two packets.    By
          prefixing the first <CR> with <CTRL-V>, the operator sends it all
          at once, but maintains the <CR> in the text.   The pass character
          can be changed to any ASCII character by the command PASS.


          QRA or help for My path's fallen, and it can't get up

               QRA ("Who are you") pinging is supported in release 1.1.8. A
          QRA ping  polls all of the  TNCs within range.   Each TNC hearing
          the  QRA ping will transmit its identification packet within 1 to
          16. This technique provides  the names of all reachable  TNCs and
          digipeaters  to the  new,  roving,  and emergency-use  packeteer.
          Also see "ANSWRQRA" command.

               Note that the  QRA function will not  work if there are  any
          digipeaters in the  UNPROTO path.   This somewhat,  but not  com-
          pletely,  helps limit  a malevolent  user's ability  to seriously
          harm the network.

               Sending QRA ping:

               1) Set the unprotocol callsign to QRA
                    cmd: UNPROTO  QRA<cr>

               2) Manually send an unconnected packet
                    cmd: CONVERSE<cr>
                    <cr>
                    ^C
                    cmd:







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          Tucson Amateur Packet Radio                   TNC 2 System Manual

               3) In 1-16 seconds, if MONITOR is ON you should be receiving
          packets empty identification  packets from other  connectable and
          compatible TNCs.

                    WB9FLW>ID:
                    AD7I>ID:
                    W5DID>ID:












































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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Chapter 5  OPERATION II:  FURTHER DETAILS


          This  chapter describes some aspects of packet operation that you
          don't  need  to be  concerned  with  for everyday  conversational
          operation.   You  will want  to consult  this chapter if  you are
          using  your station for  special applications such  as a computer
          Bulletin  Board, binary file transfers, or a "host" program.  You
          will also  find some of  this material  useful if  you intend  to
          operate on  HF or OSCAR, or  if your radio has  special timing or
          other requirements.  Even if you don't have any of these applica-
          tions, you may enjoy exploring the capabilities of your TNC.

          We  will use  the  term  "computer"  to  refer  to  computers  or
          terminals.   In the command examples, the TNC's prompts and other
          messages  are shown in ordinary type, your responses are shown in
          bold face,  and received packets are shown  underlined.  Commands
          and  other special keywords are  shown in upper  case; other text
          entered to the TNC is shown in upper and lower case.


          Special Characters

          The  TNC recognizes  a  number of  special  characters for  input
          editing, flow  control,  and other  control functions.   You  can
          change any of these  special characters to customize your  TNC to
          suit your applications, your computer, or your whim.  Most of the
          characters are set by commands  which specify the ASCII character
          code  for the  desired character.   You  can disable  any special
          character feature by  setting the  character value to  0.   Input
          editing  characters may be disabled with no serious effects.  You
          should use caution  in disabling the flow-control or Command Mode
          entry  characters.    Also be  careful  not  to  set two  special
          characters to the same value.

          Special  characters are  normally  set to  various control  char-
          acters.  Control characters are entered by holding down a special
          control key while typing another key.  For example, control-C, or
          <CTRL-C>  is entered by holding down the control key while typing
          C.  If your computer doesn't have a special control key, you will
          have to consult your computer's documentation to see how to enter
          these characters.   If you will have  difficulty entering control
          characters,  you  can  change  the  special  characters  to,  for
          example, seldom-used punctuation.

          The action of each special character is described in detail under
          the entry in Chapter 6 for the command that sets that character.

          You can enter the code for a character in either hex (base 16) or
          decimal notation.   The TNC displays character  codes in hex.   A

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          number  in hex notation is indicated by beginning the number with
          a $.  The "digits" of a hex number represent  multiples of powers
          of 16.  The values 10 through 15 are represented by the letters A
          through F, which may be upper or lower case.  For example,

                    $1B = 1 x 16 + 11 = 27.

          Tables of ASCII  character codes are  available in most  computer
          manuals.  A table of ASCII codes for control characters follows.


                 Table 5-1.  ASCII Codes for Control Characters.

          Dec  Hex  Control  Mnemonic      Dec  Hex  Control  Mnemonic

            0  $00  <CTRL-@>    NUL         16  $10  <CTRL-P>    DLE
            1  $01  <CTRL-A>    SOH         17  $11  <CTRL-Q>    DC1
            2  $02  <CTRL-B>    STX         18  $12  <CTRL-R>    DC2
            3  $03  <CTRL-C>    ETX         19  $13  <CTRL-S>    DC3
            4  $04  <CTRL-D>    EOT         20  $14  <CTRL-T>    DC4
            5  $05  <CTRL-E>    ENQ         21  $15  <CTRL-U>    NAK
            6  $06  <CTRL-F>    ACK         22  $16  <CTRL-V>    SYN
            7  $07  <CTRL-G>    BEL         23  $17  <CTRL-W>    ETB
            8  $08  <CTRL-H>    BS          24  $18  <CTRL-X>    CAN
            9  $09  <CTRL-I>    HT          25  $19  <CTRL-Y>    EM
           10  $0A  <CTRL-J>    LF          26  $1A  <CTRL-Z>    SUB
           11  $0B  <CTRL-K>    VT          27  $1B  <CTRL-[>    ESC
           12  $0C  <CTRL-L>    FF          28  $1C  <CTRL-\>    FS
           13  $0D  <CTRL-M>    CR          29  $1D  <CTRL-]>    GS
           14  $0E  <CTRL-N>    SO          30  $1E  <CTRL-^>    RS
           15  $0F  <CTRL-O>    SI          31  $1F  <CTRL-_>    US
                                           127  $7F  <DELETE>


          Operating Modes

          The TNC has  three operating modes.   We discussed  two of  these
          modes, Command Mode and  Converse Mode, in Chapter 4.   The third
          mode,  Transparent Mode,  is a  data-transfer mode  like Converse
          Mode  but is  intended  primarily for  computer data  interchange
          rather than human conversation.   We describe all three  of these
          modes below.  Additionally, the  firmware supports the KISS (keep
          it simple, stupid) mode.  Limited information is supplied here in
          the description  of the KISS command.  A description of this mode
          may  be found  in  the proceedings  of  the Sixth  ARRL  Computer
          Networking Conference.   Effective  with firmware version  1.1.8,
          the  TAPR firmware  supports a host  mode.   At the  time of this
          writing,  this  was  still   somewhat  experimental  and  is  not
          described herein.  Contact TAPR for further information.


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Command Mode

          Command  Mode is  used to  enter commands  which alter  the TNC's
          operating parameters.   The other modes are entered  from Command
          Mode.  When the TNC is in Command Mode, the Command Mode prompt,

                    cmd:

          is  printed at the beginning of  each input line.  Note, however,
          that  if the TNC has  received and displayed  packets, the prompt
          may have scrolled off the screen.

          The TNC will be in Command Mode after a reset or power-up.  After
          a power-off,  power-on sequence, all operating  parameters of the
          TNC  are  re-initialized  to  the  parameter  stored  in  battery
          backed-up  RAM (bbRAM) by the resident software.  After the RESET
          command  is  issued all  operating  parameters are  reset  to the
          default  values stored in EPROM.   The values  of most parameters
          are stored in  a permanent but easily  changed form in the  bbRAM
          memory.

          The following commands set special characters which are active in
          Command  Mode.   Refer to  the discussions  of these  commands in
          Chapter  6  for details  on the  operation  of the  characters in
          Command Mode.  Also  see the section on special  input characters
          in Chapter 4.

               CANLINE        Cancel current line
               CANPAC         Cancel output (Command Mode function only)
               DELETE         Character deletion
               PASS           Insert following special character
               REDISPLA       Re-display current line
               START, STOP    User's flow control characters (sent to TNC)
               XOFF,  XON          TNC  flow  control  characters (sent  to
          terminal)

          The following  commands enable display features  which are active
          in Command Mode.   Refer to the discussions of  these commands in
          Chapter 6 for  details on  the operation of  these characters  in
          Command  Mode.  Also see the section on terminal configuration in
          Chapter 4.

               AUTOLF         Add <LF> after <CR> in data sent to terminal








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               BKONDEL        Echo after character deletion
               ECHO           Automatic echo of serial port input
               FLOW           Type-in flow control
               LCOK           Lower case translation
               NUCR           Nulls after <CR>
               NULF           Nulls after <LF>
               NULLS          Null count
               SCREENLN       Automatic <CR> insertion


          Entering Data-Transfer Modes

          There are several ways to enter a data-transfer mode from Command
          Mode.  You can type the command CONVERS to enter Converse Mode or
          the command TRANS  to enter  Transparent Mode, and  the TNC  will
          immediately enter the specified mode.  The TNC will automatically
          enter  a data-transfer  mode if  you are  in Command Mode  when a
          connection is  completed.  You can specify the data-transfer mode
          for automatic entry with the command CONMODE:

                    cmd:CONMODE TRANS

          will specify Transparent Mode, and

                    cmd:CONMODE CONVERS

          will return to the default choice of Converse Mode.

          The timing of the automatic entry into data-transfer mode depends
          on  whether you or the  other station initiated  the connection. 
          If you receive a connect request which your TNC accepts, you will
          enter  data-transfer   mode  when  the  TNC   sends  the  connect
          acknowledgment  (ACK)  and types  the  message  *** CONNECTED  TO
          <callsign>.

          If  you initiate the connection with the CONNECT command, you can
          control the timing of  the mode change with the  command NEWMODE.
          If  NEWMODE is OFF, the mode will  change when the connect ACK is
          received  and the *** CONNECTED TO:  <callsign> message is typed.
          If  NEWMODE is ON, you will enter data-transfer mode immediately,
          without  waiting for a successful  connection.  Any  text sent to
          the TNC  at this point  will be queued  up in packets  which will
          wait  for  a successful  connection before  being  sent.   If the
          connect attempt fails, you will be returned to Command Mode.  You
          will also be returned  automatically to Command Mode when  either
          station disconnects and ends the QSO.





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          Converse Mode

          The data mode used most often for ordinary QSOs is Converse Mode.
          In  Converse Mode, the information  you type is  assembled by the
          TNC into packets and transmitted over the radio.  The send-packet
          character causes the input to be packetized for transmission.  If
          you  type a full  packet-length of characters  without typing the
          send-packet  character,   your  input  will  be   packetized  and
          transmitted anyway.

          The default send-packet  character is <CR>,  but you can  specify
          any  character with the command SENDPAC.   You may also choose to
          have  the send-packet character transmitted in the packet or not.
          If the send-packet character is <CR> it is  natural to include it
          in the packet as part of the text as well as interpreting it as a
          command.  This is accomplished by setting CR ON.  If you use some
          other character to force packet transmission, you may want to set
          CR OFF and inhibit transmission of the send-packet character.  If
          you set the  send-packet character to something  other than <CR>,
          you  can  cancel  packets   of  more  than  one  line   with  the
          cancel-packet character,  which is  set with the  command CANPAC.
          Single-line packets  can be canceled with  either the cancel-line
          character or the cancel-packet character.

          To  return to Command  Mode from Converse Mode  you must type the
          Command Mode entry  character, or  send a BREAK  signal over  the
          serial port.   A BREAK is  not a regular ASCII  character, but it
          can  frequently be  transmitted by  typing a  special key  on the
          keyboard.

          A BREAK signal is a  continuous mark (or 1) signal on  the serial
          port Transmit  Data line  lasting approximately  0.2 second.   In
          fact, the  timing of the signal  is not very  important, and most
          serial  ports will  recognize a  BREAK if  the mark  signal lasts
          significantly  longer  than the  time  required  for a  character
          transmission.  Because of the simple nature of this signal, it is
          easily possible  to generate a  BREAK with circuitry  external to
          the computer, thus  guaranteeing entry to  Command Mode in  auto-
          matic station operation.

          The following commands set special characters which are active in
          Converse  Mode.  Refer to  the discussions of  these commands for
          details on the operation of the characters in Converse Mode.








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               CANLINE        cancel current line
               CANPAC         cancel current packet
               COMMAND        Command Mode entry
               DELETE         character deletion
               MFILTER       characters to be filtered in monitored        
                        packets
               PASS           insert following special character
               REDISPLA       re-display current line
               SENDPAC        send current packet
               START, STOP    user's flow control characters (sent to TNC)
               XOFF,  XON          TNC  flow  control  characters (sent  to
          terminal)

          The following  commands enable display features  which are active
          in Converse Mode.  Refer to the discussions of these commands for
          details on the operation of these characters in Converse Mode.

               8BITCONV      Retain high-order bit from serial port        
                              in converse mode
               AUTOLF         Add <LF> after <CR>
               BKONDEL        Echo after character deletion
               ECHO           Automatic echo of serial input
               ESCAPE         <ESCAPE> translation
               FLOW           Type-in flow control
               LCOK           Lower case translation
               NUCR           Null characters after <CR>
               NULF           Null characters after <LF>
               NULLS          Null count
               SCREENLN       Automatic <CR> insertion


          Transparent Mode

          Packet  radio is  very well  suited to  transfer of  data between
          computers.   In  some  cases Converse  Mode  will work  well  for
          computer data transfer.  However, files  such as a .CMD file on a
          CP/M system, a BASIC program, or even a word-processor text file,
          may contain characters which  conflict with special characters in
          Converse Mode.  Some of these files may utilize all eight bits of
          each byte rather than the seven bits required by ASCII codes.  If
          you transfer such files you will have to use Transparent Mode.

          Transparent  Mode is a data-transfer mode like Converse Mode.  In
          this  mode there are no special characters -- everything you type
          (or  everything your computer sends  to the TNC) is sent over the
          radio exactly as it was  received by the TNC.  There are no input
          editing features and there is no  send-packet character.  Packets
          are sent  at regular  time  intervals or  when a  full packet  of
          information  is  ready.   The  time  interval  at  which data  is
          packetized is set by the PACTIME command.

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          The  display characteristics  of  the TNC  are  also modified  in
          Transparent Mode.  Data is sent to the computer exactly  as it is
          received  over the  radio,  including all  8  bits of  each  byte
          received.   Features such  as auto-linefeed insertion  and screen
          wrap  are disabled, and echoing  of input characters is disabled.
          The parameters  that control these  features in Command  Mode and
          Converse Mode are not changed  by entering Transparent Mode,  and
          all display features are  re-enabled when the TNC is  returned to
          Command Mode.   Most of  the link status messages  that appear as
          the TNC moves between disconnected  and connected states are also
          disabled in Transparent Mode.

          In  order  to  permit the  Command  Mode  entry  character to  be
          transmitted  freely in  Transparent Mode,  the escape  to Command
          Mode  from  Transparent   Mode  has  been  made   a  little  more
          complicated.   You  can still  return to  Command mode  by trans-
          mitting  a BREAK signal, just as in  Converse Mode.  You can also
          utilize the Command Mode entry character in the following way.

          You  must wait for a time  period after typing the last character
          to be sent.  This time is set by the  command CMDTIME.  Following
          this  wait, you  must type  three  Command Mode  entry characters
          (default  <CTRL-C>) within  an  interval CMDTIME  of each  other.
          After  a final CMDTIME interval in which no characters are typed,
          you will see the

                    cmd:

          prompt.  If any  characters are typed during this  interval (even
          Command Mode entry characters) the escape will be aborted and all
          the  Command Mode entry characters  that have been  typed will be
          sent as packet data.   If you set CMDTIME to zero you will not be
          able  to   escape  from   Transparent  Mode  using   this  second
          procedure.


          Flow Control

          Whenever  data is  transferred  to computers  (home computers  or
          TNCs), there  is a chance that  the data will be  received faster
          than the computer can handle it.  Some programs try  to deal with
          this by  providing data buffers  for storing incoming  data until
          the program is ready for it.  However, this merely postpones  the
          problem, since there is a  limited amount of room in  any buffer.
          In order  to prevent loss  of data the  computer must be  able to
          make whatever is sending data stop  sending, and later tell it to
          resume sending. If you are a home computer user, you are probably
          already  familiar with one type of flow control, which allows you
          to  stop the  output  from the  computer  while you  read  it and
          restart it when you are ready for more.

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          The  TNC's input buffer may fill up in Command Mode if you try to
          type too long a command.  In Converse Mode the buffer may fill up
          for any  of several reasons:   you may  be using a  faster serial
          port baud rate than the radio data rate;  radio data transmission
          may have  slowed down  because of  noise  or other  users on  the
          channel; the person or computer at the other end may have stopped
          output from that TNC.   The TNC will signal the computer  to stop
          sending data when there is room remaining for about 80 characters
          in the buffer.   When the buffer fills up  entirely, data will be
          lost.  When the buffer empties so that there is room for at least
          270 characters, the TNC will signal the computer to start sending
          data again.

          A  computer file transfer program  may be unable  to process data
          fast enough to keep up with output  from the TNC.  In order to be
          sure of  reading  every character,  a  computer must  respond  to
          interrupts from its I/O  devices.  Some simple programs  may poll
          the input  register for  new data.   If the  polling is  not done
          often  enough,  data  may  be   lost.    Some  computers  disable
          interrupts during disk accesses.  If the program enters a routine
          which  will not allow it to  check for data or  respond to it, it
          should signal the TNC to stop sending data.

          There  are  two  methods  of providing  flow  control  which  are
          supported  by the TNC.   XON/XOFF flow  control, sometimes called
          "software  flow control,"  is accomplished  by sending  a special
          character (usually  <CTRL-S>) to request that the output stop and
          another special  character (usually <CTRL-Q>)  to restart output.
          Hardware flow control may be used if both computers use the Clear
          To Send (CTS) and Data Terminal Ready  (DTR) lines of the RS-232C
          standard. 

          Some commonly  used terminal programs and  file transfer programs
          for home computers do not implement flow control in software, and
          many serial ports do not support hardware flow control.  Although
          the DTR  and CTS lines appear  at the connector, they  may not be
          used on some computers unless the software reads the state of the
          CTS line.   If you find  that the TNC  seems to lose  data during
          file  transfers, you  should immediately  suspect a  flow control
          problem.


          XON/XOFF Flow Control

          If you are  using a terminal (rather than a  computer) or if your
          computer does  not support DTR/CTS  flow control, you  should use
          XON/XOFF flow control, which is enabled by setting XFLOW ON.  The
          special flow control characters are set to <CTRL-S>  and <CTRL-Q>
          by default, but they may  be changed.  The commands XON  and XOFF
          set the characters which will be sent to the terminal by the TNC,

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          and the  commands START and STOP set the characters to be sent to
          the TNC by the terminal.  Your  computer may receive as many as 4
          characters from  the TNC after  sending a  STOP character,  since
          some  characters may  already be  "in  route" through  serial I/O
          chips.

          If  you  send a  STOP (START)  character to  the  TNC when  it is
          already stopped (started), the character will be ignored.  If the
          STOP and START character  are the same character, this  character
          will "toggle" the output,  turning it off if it is  on, and on if
          it is off.

          You  can disable XON/XOFF flow  control in one  direction only by
          setting the appropriate flow control characters to 0.   If you do
          this, the TNC  will automatically  use CTS flow  control to  stop
          input from  the  terminal.   XON/XOFF  flow control  is  normally
          disabled in Transparent Mode, since all characters are treated as
          data.  If you cannot use DTR/CTS flow control, you may enable the
          XON  and  XOFF  characters (the  commands  from  the  TNC to  the
          terminal) by setting TXFLOW ON and XFLOW ON.  The  START and STOP
          characters (the commands  to the  TNC from the  terminal) can  be
          enabled in  Transparent Mode by setting TRFLOW ON.  Note that the
          mode  is  no longer  truly  transparent when  these  features are
          enabled.


          Hardware Flow Control

          Hardware flow control is less likely to depend on the programming
          of  a  particular  communications program.      DTR  and CTS  are
          normally  used for flow control signals in Transparent Mode.  The
          command XFLOW OFF  enables hardware flow control in Converse Mode
          and  Command Mode.    Your  computer may  receive  as many  as  2
          characters after it signals  the TNC to stop sending,  since some
          characters may already  be "in route"  through serial I/O  chips.
          Refer  to Chapter  7,  Hardware  for  details  on  the  interface
          required for hardware flow control.


          Type-in Flow Control

          Type-in  flow control, enabled with the command FLOW, is really a
          display feature.  It can keep the TNC from interrupting you  with
          incoming packets when you are  in the middle of typing  a command
          line or an outgoing packet.  As soon as you type the first  char-
          acter of a line, the  TNC will put a "hold" on all output (except
          for echoing your input).  The "hold" remains  in effect until you
          type a  <CR> to end the command  line, or a send-packet character
          to mark the end of a packet, or until you erase or re-display the
          line you have started.

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          Some   computers  have  difficulty   simultaneously  sending  and
          receiving characters over the serial port.  This is most commonly
          the  case for  computers  with "software  UARTs."   Type-in  flow
          control will  improve the  operation of such  computers with  the
          TNC.


          Packet Operation

          The previous chapter's  discussion of "Basic Operation"  contains
          enough  information  for most  packet  operation.   This  section
          describes a few other aspects of packet operation.


          Station Identification

          Your station  identification (call sign) is set  with the command
          MYCALL, as described  in the previous chapter.  If  you will have
          more than one  station on the  air operating  with the same  call
          sign,  they must  be distinguished  -- no  two stations  can have
          identical station  identifications, or the  packet protocol  will
          fail.   You can  distinguish additional stations  by setting  the
          "secondary station ID", or SSID.  This  is a number from 0 to 15,
          appended to the call sign with a dash:

                    cmd:MYCALL W3IWI-3

          If you  don't specify the SSID  extension, it will be  0, and the
          TNC  won't explicitly  show SSIDs  that are  0.   If you  want to
          connect to a  station with a  SSID other  than 0, or  use such  a
          station as a digipeater, you must specify the SSID:

                    cmd:CONNECT AD7I-2
               or
                    cmd:CONNECT WA7GXD VIA N7CL-5

          The TNC can  send an automatic identification  packet every 9-1/2
          minutes  when your station is operating as a digipeater.  You can
          enable this  feature with the  command HID ON.   An ID  packet is
          displayed as follows by a monitoring station:

                    W3IWI-3>ID:W3IWI/R

          You can request a  final identification as you take  your station
          off  the  air with  the  command  ID.   The  TNC  will only  send
          identification packets if it has been digipeating.


          Automatic Operations


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Normally,  any packet station can  be used by  other stations for
          relaying, or  digipeating, packets to a  more remote destination.
          If  you don't want your station digipeating packets, you can give
          the   command   DIGIPEAT  OFF.      Unless   there  are   special
          circumstances, such  as a  station operating on  emergency power,
          most  packet operators set DIGIPEAT  ON in the  spirit of Amateur
          cooperation.

          Your station  will normally accept a connect request from another
          station  if it  isn't already  connected.   You can  disable this
          capability  by setting  CONOK  OFF.   If  you receive  a  connect
          request when CONOK is OFF, the TNC will display the message

                    *** connect request: <callsign>

          and send a "busy  signal" rejection packet to the  other station.
          If you  receive a  rejection packet  from a  station  you try  to
          connect to, your TNC will display

                    *** <callsign> busy
                    *** DISCONNECTED

          If  you  want to  have a  special  message sent  automatically to
          stations  connecting to you, you can specify the message with the
          command CTEXT.  This message can consist of any text string up to
          120  characters, and you may include <CR>s by prefixing them with
          the pass character:

                  cmd:CTEXT Sorry, I can't talk right now.<CTRL-V><CR>
                  I'll be on the air again after 8 PM.<CTRL-V><CR>
                       Joe

          In order  for this message to  be sent to  stations connecting to
          you, you must  set CONOK  ON so that  the connection takes  place
          (default), and enable the automatic message with CMSG ON.

          If you want to leave you station on but inhibit transmitting, you
          can set XMITOK OFF.  If you do this, you would normally set CONOK
          OFF as well.

          You can have  your station periodically send an automatic message
          by   enabling  "beacons."    A   beacon  can  be   used  to  make
          general-interest   announcements,   provide  packets   for  other
          stations to use to test their ability to receive, or announce the
          presence of  a bulletin-board operation.   The beacon  message is
          set with the command BTEXT, which works the same way as the CTEXT
          command.  You enable beacon transmission and set the frequency at
          which beacons are sent with the command BEACON.  To  transmit the
          beacon  at 10-second intervals, for example, give the command


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                    cmd:BEACON EVERY 1

          The beacon  function also has  a transmit-after mode,  enabled by
          using  the keyword  AFTER in place  of EVERY,  in which  a beacon
          packet  is  only transmitted  after  activity  is  heard  on  the
          channel.  This feature might be used to leave an announcement for
          other  packet users.  If  someone transmits on  an otherwise idle
          channel, a beacon can be sent a short time later.  No beacons are
          sent in this mode  if there is  a lot of  packet activity on  the
          channel, since the required period of quiet will not occur.


          Packet Formatting

          The  maximum  length of  a packet  is  determined by  the command
          PACLEN.  If you  type more than the maximum  number of characters
          without entering a send-packet character, the TNC will transmit a
          maximum-length  packet.   In Transparent  Mode, a packet  will be
          sent  if the maximum number  of characters is  entered before the
          delay conditions set by PACTIME force a packet to be  sent.  Some
          TNCs   may  not  be  able  to  accept  packets  longer  than  128
          characters.

          If you have set  the send-packet character to <CR>,  you probably
          want  the <CR> to  be included in  the packet for  display at the
          other end.   If you set  the send-packet character  to a  special
          non-printing  character, you  probably want  the character  to be
          treated as a command only.   The command CR controls whether  the
          send-packet character is to be echoed and included in the packet.

          You can  add a <LF> after  each <CR> included in  your packets by
          setting LFADD ON.   If the other  station reports that lines  are
          overprinted  on his display, and he can't remedy the situation at
          his end, you can enable this function.


          Commands Affecting Protocol

          This  section describes  some  of the  commands  that affect  the
          operation  of the packet protocol.   Details of  the protocol are
          given in Chapter 9.

          The  TNC implements AX.25  Level 2 protocol,  a set of  rules for
          formatting messages  to other TNCs.  The version of AX.25 Level 2
          protocol  used by  the TNC  can be  set to  Version 2.0  with the
          command  AX25L2V2 ON, or to Version 1.0 with the command AX25L2V2
          OFF.  Digipeating may not be successful if  some TNCs are running
          Version 1.0  and some are running Version  2.0.  In addition, the
          command  CHECK controls  a timing  function  that depends  on the
          protocol version selected.

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          You can specify the "address" to be used for unconnected packets,
          as  well as  intermediate digipeaters  with the  UNPROTO command.
          The format is similar to that of the CONNECT command:

                    cmd:UNPROTO QST VIA NK6K

          The default address for unconnected packets is CQ.

          The following  functions may be useful for tracking down protocol
          problems.  They are seldom useful for ordinary packet operations.
          The  error-checking  function of  the  protocol  is disabled  for
          monitored packets with the  command PASSALL.  If you  set PASSALL
          ON,  any "packet"  will be  displayed if  it meets  the following
          conditions:   It must  start with  a flag  sequence; and  it must
          contain an integral  number of  8-bit bytes.   The TRACE  command
          enables the display of the address and control fields of packets,
          as well  as the text.   The trace function displays  all bytes in
          hex as well as ASCII equivalents.


          Packet Timing Functions

          Transmit Timing

          Amateur  radio  equipment  varies  greatly  in  the  time  delays
          required in switching from receive to transmit and from  transmit
          to   receive.    If  the  TNC  starts  sending  data  before  the
          transmitter is operating or  before the receiver has had  time to
          switch  from transmitting and lock up on the incoming signal, the
          packet will not be  received properly.  The delay  between trans-
          mitter keyup and the beginning of data transmission is controlled
          by the  command TXDELAY.  During  the time the TNC  is keying the
          transmitter   but  not   sending   data,  it   will  transmit   a
          synchronizing signal (flags).

          If you  are transmitting packets  through an audio  repeater, you
          may require a  considerably greater keyup delay  than is required
          for direct communications.  Furthermore, the extra keyup delay is
          not required if the repeater has not had time to "drop" since the
          last transmission. The  command AXDELAY allows you to  specify an
          additional  keyup  delay  to  allow  the  repeater  receiver  and
          transmitter to lock up.  The command AXHANG sets the time the TNC
          will assume is required for the repeater to drop.  If the TNC has
          detected channel  activity  recently  enough  that  the  repeater
          transmitter should still  be on,  it will wait  only the  TXDELAY
          time before sending data,  rather than adding an AXDELAY  time as
          well.
          The  commands TXDELAY, AXDELAY, and AXHANG all set times in units
          of 10 ms.  If AXDELAY is in effect the total keyup delay will be


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

               Keyup delay = (TXDELAY + AXDELAY) * 10

          in  milliseconds.    If  channel  activity  has  been heard  more
          recently than AXHANG*10 ms ago, the keyup delay will only be

               Keyup delay = TXDELAY*10

          in milliseconds.


          Packet Timing

          The  AX.25 protocol  provides  for retransmitting  packets if  no
          acknowledgment  is heard  from  the intended  destination station
          within  a  certain  period  of  time.    A  packet  might not  be
          acknowledged  due to  channel noise  or "collision"  with another
          packet transmission, and since there may be other stations on the
          channel, the receiving station may not be able to acknowledge the
          received  packet   immediately.    The  time   lapse  before  the
          originating station retransmits the packet is  set by the command
          FRACK  (frame   acknowledge  time).     The  maximum   number  of
          retransmissions before  the  originating station  terminates  the
          connection is set by  the command RETRY.   The maximum number  of
          transmissions  of   a  packet  is  RETRY+1,   since  the  initial
          transmission does not count as  a retransmission.  Setting  RETRY
          to 0 specifies an infinite number of retries.

          The  frame-acknowledge time  is  automatically corrected  for the
          additional  time required  for digipeating.   The  time in-terval
          before TNC 2 retransmits an unacknowledged packet is 

               Retry interval = FRACK * (2*n + 1)

          in seconds,  where n is the number of digipeaters in use for this
          connection.

          Acknowledgments of digipeated  packets are made from  end to end,
          and  digipeaters do not acknowledge  the packets they  relay.  If
          there  are several intermediate relays, the  chance of either the
          original  packet or the acknowledgment to be lost increases dras-
          tically.  To reduce  this problem, an automatic wait time  can be
          imposed  on any  station  not transmitting  a digipeated  packet.
          Stations waiting for a clear channel to transmit packets wait for
          this time interval after  the channel clears before transmitting.
          This wait does not  apply if the station will be transmitting one
          or  more digipeated packets.  This usually gives the digipeater a
          clear chance at the channel.
          The wait time is set by  the command DWAIT, which specifies 40 ms
          intervals.   If  no digipeating  is being done  by anyone  in the
          local area,  this parameter can be set to 0,  but in any event it

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          should  be set to the same value by all members of a local packet
          group.

          In  order to avoid unnecessary packet retries, the TNC implements
          a  collision-avoidance  strategy  which  applies  to all  packets
          except  those being  digipeated.   On the  second and  subsequent
          transmissions of a particular packet, the TNC waits an additional
          random  time after  detecting  a clear  channel before  beginning
          transmission.  This prevents repeated collisions of transmissions
          by the same two stations.   The random time is a  multiple (0-15)
          of the TXDELAY time.

          The  interval,   in  milliseconds,  between  the   TNC  detecting
          carrier-drop and beginning to transmit is

               Wait time = DWAIT * 10

          for  the   first  transmission  of  a  packet.    For  subsequent
          transmissions of the same packet the interval is

               Wait time = DWAIT * 10 + ( r * TXDELAY ) * 10

          where r is a  random number from 0 to  15.  Thus, if your  TNC is
          forced  to  re-transmit packets,  you  will  occasionally hear  a
          fairly long delay before transmission begins.

          Multiple  packets  may  be  transmitted  before  waiting  for  an
          acknowledgment.   This  permits more  efficient channel  use when
          large  amounts of data are being transferred.  The maximum number
          of  packets   which  the  TNC   will  send  before   waiting  for
          acknowledgment is specified  by the command MAXFRAME.   This does
          not mean that  the TNC will wait until  several packets have been
          entered before  transmitting.   MAXFRAME in combination  with the
          command  PACLEN, which sets the maximum number of characters in a
          packet, determines how much  information can be sent in  a single
          transmission.   The best combination for  efficient data transfer
          is determined partly  by the  channel quality and  partly by  the
          rate at which  the terminal can  process data.   For a 1200  baud
          terminal  data rate,  you  should start  with a  combination that
          produces about 300 characters outstanding at one time.


          Radio Baud Rate

          The radio data transmission rate is set by switches 6, 7 and 8 of
          DIP switch  SW2  (Do not change these switches while power is on,
          and make sure only one of these three switches is  ON at any time
          while the TNC is powered).  The rates available are:



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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                      Table 5-2.  DIP switch settings for
                               radio baud rates.

                     Radio Data Rate     SW2 Switch Setting
                          (baud)             6    7    8

                            300             ON   OFF  OFF
                           1200             OFF  ON   OFF
                           9600             OFF  OFF  ON


          Note that there is no relationship between terminal baud rate and
          radio baud rate.   In  order to communicate  with another  packet
          station you  must use the same  radio baud rates.   The length of
          time  required to send a given amount of information increases as
          the baud  rate decreases.  For  example,  it takes  four times as
          long to send data at  300 baud as at 1200 baud.  If  you use slow
          radio baud rates, you should limit the length of transmissions by
          setting  MAXFRAME to 1 and  choosing PACLEN so  that the hardware
          watchdog timer  does not  disrupt your transmissions  and channel
          traffic is broken up frequently.

          The  Bell-202 compatible modem is optimized for a 1200 baud radio
          data  rate.   For  HF operation  at low  baud  rates, you  should
          reconfigure  the modem as described  in Chapter 7.   The on-board
          modem is not useful at rates higher than 1200  baud.  The TNC can
          provide  data  signals at  9600 baud,  but  an external  modem is
          required for such operation.


          Special Protocol Times

          You can set up a connection timeout with the command CHECK, which
          specifies  a  time  in  multiples of  10-second  intervals.  This
          function  prevents your  TNC from getting  stuck in  a connection
          when the other station  disappears for longer than the  specified
          time.  The TNC  uses this time somewhat differently  depending on
          the setting of AX25L2V2.

          The command RESPTIME sets a delay between the receipt of a packet
          and the transmission of the acknowledgment packet.  This delay is
          used to  prevent collision between an  acknowledgment and another
          packet  from the sending  station.   This is  primarily necessary
          during  file transfers;  otherwise the  delay is  best set  to 0.
          During file  transfers the stations receiving the file should set
          RESPTIME to 10 or 12 (default).

          The  timing  of  packet   transmission  in  Transparent  Mode  is
          determined by the command PACTIME.  You can choose the way packet
          transmission is  timed.   If you  are typing  input  to a  remote

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          computer  it  is usually  best  to  have packets  transmitted  at
          regular intervals.  If  your computer is operating  a remote-host
          or bulletin  board  program  you  should send  packets  after  an
          interval with no further input from the computer.  You can enable
          the use of PACTIME in Converse Mode with the command CPACTIME.


          Monitor Functions

          The TNC's protocol is designed  for setting up "circuits" between
          two  stations.   However  it  can also  operate  in a  mode  more
          suitable  for a  "net" or  "round-table" discussion  with several
          participants, although reliable reception of all transmissions by
          every station cannot be guaranteed.  This is done by enabling the
          monitor functions.   Most of the monitor  functions are described
          in Chapter 4.

          Monitoring  is enabled  by the  command MONITOR ON,  and separate
          monitor functions are individually enabled.

          If connected packet  QSOs are  taking place on  the frequency  of
          your group  conversation, you  may wish to  ignore all  connected
          packets  while  your group  operates  in unconnected  mode.   The
          command MALL OFF causes the TNC to ignore connected packets.

          If you  want to  be  able to  monitor packet  activity when  your
          station is  not connected, but have  all monitoring automatically
          cease when you connect to someone, set MCON OFF.

          If you want  to monitor stations  selectively, you  can set up  a
          list  of up  to  eight callsigns  with the  command LCALLS.   The
          callsigns  in this list are regarded as "buddies," i.e., the only
          stations you want to listen to  if BUDLIST is ON.  Otherwise, the
          stations in the list will be ignored, and all other stations will
          be monitored.

          You  can operate a group conversation with some data integrity by
          having the stations connect in pairs and setting MALL ON and MCON
          ON.  This does not insure  that every packet is received at every
          station, but it does insure that a packet involved in a collision
          will  be  retried.    If  you  have an  odd  number  of  stations
          participating  in  this sort  of  conversation,  one station  can
          connect to himself via another station as digipeater.

          For example,  WB6YMH, WD0ETZ,  WA0TTW, W1BEL,  and  K9NG wish  to
          carry  on  a group  conversation.    In  order  to make  all  the
          transmissions as reliable as possible, the  following connections
          are made.

               WB6YMH connects to W1BEL

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

               WA0TTW connects to K9NG
               WD0ETZ connects to WD0ETZ via W1BEL

          If each station specifies MCON ON and MALL ON, each  station will
          see the packets sent by all the others.

          Ordinarily, only text packets are displayed.   If you want to see
          some of the  protocol packets, you can  set MCOM ON and  connect,
          disconnect, disconnect acknowledgments,  and DM  (connect-request
          rejection) packets will be displayed.  For example,

                    WB9FLW>N7CL <C>
                    KV7B>N2WX <D>

          indicate  connect   and  disconnect  packets.     Disconnect  ac-
          knowledgments are designated <UA>, and DM packets are <DM>.

          You  can cause  the  TNC  to  "filter"  certain  characters  from
          monitored packets with the  command MFILTER.  This allows  you to
          remove, for example, form-feeds,  bell characters, or extra <LF>s
          that may be necessary  to the stations involved in  a connection,
          but which may interfere with your display.  You can specify up to
          four characters by  giving the  ASCII character codes  in hex  or
          decimal.


          Real-Time Clock and Time Stamping

          You can enable the TNC's real-time  clock by setting the date and
          time with the command DAYTIME.   Once you have set the clock, you
          can request the time by entering DAYTIME with no parameters.  The
          format  of date  and time  display is  controlled by  the command
          DAYUSA.   If  the TNC  is powered  off, DAYTIME  will have  to be
          reset.

          Monitored packets  can be time-stamped  if DAYTIME has  been set.
          To enable this function, set MSTAMP ON.  You can  also time-stamp
          connect and disconnect messages with the command CONSTAMP ON.


          HF and OSCAR

          The TAPR TNC 2 is optimized for a local VHF FM environment:   The
          modem is configured for best response at 1200 baud.  The settings
          of MAXFRAME  and PACLEN provide  the possibility of  several con-
          tinuous frames of long data length.

          The requirements  for optimum performance  with a  typical HF  or
          OSCAR 10 path are  very different.  Lower signal  to noise ratios
          require lower baud  rates, noise spikes and fades require shorter

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          packet lengths, and a higher rate of false carrier detects lowers
          the  total usable  dynamic range  in the  audio input.   The  TNC
          hardware and  software can be reconfigured  to improve throughput
          in  these environments.    For  HF  operation  at  300  baud,  we
          recommend setting MAXFRAME to 1.

          The TNC  detects  a busy  channel by  monitoring the  lock-detect
          signal  from  the demodulator.    The presence  of  a lock-detect
          signal  is indicated by the Data  Carrier Detect (DCD) LED.  Each
          time DCD  goes off the TNC will start a DWAIT interval which must
          elapse before  the channel is considered  to be available.   On a
          noisy channel spurious lock-detect signals may be generated.  For
          HF  and OSCAR operation  you should set  DWAIT to 0.   The random
          wait  before  retry  transmissions  can be  disabled  by  setting
          TXDELAY 0 and using AXDELAY to  set the required keyup delay.  Of
          course, AXHANG should be 0 for this application.

          If you  are operating  a full-duplex radio  station (simultaneous
          transmit and receive) such as an OSCAR 10 station, you should set
          FULLDUP  ON.   The  TNC is  always  electrically capable  of full
          duplex  operation,  but this  parameter  causes  the protocol  to
          behave differently  in acknowledging  packets.  In  addition, the
          TNC will  ignore the state of the  DCD line.  You  may be able to
          improve operation somewhat  by disconnecting the DCD  line at the
          modem connector (J4 pins 1-2).

          Although intuition  tells you that  lower baud rates  will reduce
          the  number of  packet retries,  there is  usually a  small range
          between "too fast" and "too slow."   A slower packet takes longer
          to transmit and is therefore a larger target for fades and static
          crashes.  The entire  packet must be received correctly  in order
          to be accepted.   Data rates of 1200 baud have  been used on both
          HF and through OSCAR 10.

          You  can improve the response of the  modem for low baud rates by
          calibrating  the modulator  and  demodulator tones  for a  narrow
          shift,  as  described in  the  next  section, and  modifying  the
          demodulator.  This also permits the use of a narrow filter by the
          receiving  station.    You  should  set  the  demodulator  center
          frequency so  that it is  midway between  the high and  low tones
          when the packet tones  are centered in your passband.   The modem
          parameters and  timing constants are  determined by the  parts on
          headers U15  and  U19.   Consult  the EXAR  notes  listed in  the
          Bibliography  for the procedure for determining component values.
          If  you are dedicating your  TNC to 300  baud operation, consider
          increasing the  time-constant of  the filter  at U20  pin 3  by a
          factor of 4 (increase the capacitor value, not the resistor).

          The  on-board modem can  be completely bypassed  at connector J4.
          You  can supply  an external  modem which  uses  other modulation

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          methods or higher baud rates.  The interfaces available on J4 are
          TTL levels.  Refer to Chapter 7 for more information.


          Modem Calibration using CAL and RXCAL

          The  TAPR TNC 2 contains a versatile, user configurable FSK modem
          that  is suitable for both 1200 baud  packet use as well as lower
          data rate use, such  as 200 Hz  shift 300 baud  use on HF  links.
          Calibration of the modem  is usually only required when  the unit
          is initially  put into operation or  when you want  to change the
          modem  characteristics.  You may want to check the calibration if
          you  have difficulty  connecting  to other  packet stations,  but
          recalibration is normally not necessary.

          Calibration of the TNC on-board modem is straightforward.  First,
          determine  the data  rate at  which  you wish  to  operate.   The
          required shift may then be determined, followed by the actual FSK
          frequencies to use.  While  you may select from any tones  in the
          normal audio range, there are a few simple rules that may help.

          1.  The TNC only supports 300 baud and 1200 baud operation of the
          radio link using the  on-board modem.  While the modem is capable
          of operating  at other  data rates,  the TNC  data-rate generator
          circuit  only supplies clocks for  300, 1200 and  9600 baud (9600
          baud is for use with an external modem).

          2.  Most 1200 baud operation uses 1000 Hz shift and tones of 1200
          Hz and  2200 Hz.  These are  the default tones for  which the TNC
          modem is  optimized, using the  components supplied  in the  kit.
          However,  800 Hz  shift with  tones of  1300 Hz  and 2100  Hz may
          provide improved  operation.   This tone-pair is  compatible with
          TNCs using 1000 Hz shift modems.

          3.   Most HF operation below  28 MHz uses 300 baud,  200 Hz shift
          FSK.  TAPR  recommends 1600 Hz and 1800 Hz  as the modulator tone
          frequencies, but  any pair  of frequencies with  this separation,
          modulating an SSB transmitter,  will work.  If  your demodulation
          center frequency is 1700 Hz, your transmissions will  be readable
          whenever  you are able to  copy the other  station, regardless of
          his actual  modulation frequencies.   Incidentally,  the sideband
          may be  chosen at will  due to the  nature of the  data, although
          most stations conventionally use LSB.

          In the  example below we  will set up  the modem for  normal 1200
          baud operation with 800 Hz shift.

          The  software calibration  routine compares  the frequency  being
          calibrated  against a reference signal.  The desired frequency is
          specified by setting a count, n, using the command CALSET.

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          For the  modulator, determine the calibration  count according to
          the following formula:

                    n = (525,000 / f) + 1

          where f is the desired frequency in Hertz.  Substituting 1300 and
          2100 Hz, we end up with:

                    n = 405 (for 1300 Hz)
                    n = 251 (for 2100 Hz)

          To set the PLL  demodulator, we use the RXCAL  command, explained
          below.

          Modulator Adjustment

          The next step is to preset the trimpots for the  modulator.  When
          adjusting the trimpots, you  should hear a soft "click"  when the
          element  is  adjusted to  the  end of  its travel.    Turning the
          element past this point will not result in damage to the trimpot;
          however,  it is  suggested that  you  do not  make a  practice of
          turning  the adjustment  screw past this  point too much.   Use a
          small-tipped screwdriver or  special trimpot adjusting  tool when
          adjusting the trimpots.

          Preset R77 20 turns counter-clockwise (CCW) or until you hear the
          element "click" at full CCW rotation.  R77 controls the higher of
          the two modulator  output tones and this  sets it to  its maximum
          frequency.

          Preset R78 20 turns clockwise (CW) or until you  hear the element
          "click"  at full CW rotation.  R78  controls the lower of the two
          modulator output tones and this sets it to its lowest frequency.

          Turn off the power to the TNC and remove it from its cabinet.  To
          protect the  battery backed-up RAM, be  sure to set the  TNC on a
          non-conducting surface -- a sheet of paper will do.   Attach your
          terminal and follow  the standard power-up  procedure.  When  you
          see the command mode prompt, enter

                    cmd:CALSET 405

          or use the value appropriate for the lower modulator tone.  Next,
          enter

                    cmd:CALIBRA

          This starts the software calibration routine.  The  "commands" to
          the  calibration routine  are single  characters, and  require no
          carriage return.

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Install a push-on jumper  at JMP9 pins 1 and 6 (the  top two pins
          of JMP9 nearest C44) and another push-on jumper at JMP4.

          NOTE:    During calibration  the  STA and  CON  LEDs are  used as
          frequency indicators.  When the STA LED is glowing, the frequency
          is  too  high, go  lower.    When the  CON  LED  is glowing,  the
          frequency is too low, go higher.

          Press the  K key on  your computer.   Either the  STA or  CON LED
          should  illuminate.  Next, press  the space bar  on your keyboard
          and verify that the other  LED (CON or STA) illuminates  in place
          of the one illuminated  in the preceding step.   Press the  space
          bar again until the CON LED is illuminated.

          Slowly  rotate the  adjustment screw  on trimpot  R78 in  the CCW
          direction until both the  STA and CON LEDs illuminate.   The LEDs
          are a bit  slow to respond, so be careful when the STA LED begins
          to flicker.  You will probably notice a portion of the adjustment
          when both LEDs illuminate; set the adjustment screw to the center
          of  this band.   If  you go  too far,  only the  STA LED  will be
          illuminated; in this case, turn the adjustment screw CW.

          When  both LEDs are steadily illuminated, press  the Q key.  Both
          LEDs  should  extinguish  and  the  command  mode  prompt  should
          reappear.  The lower tone is now calibrated.

          To calibrate the upper tone, enter

                    cmd:CALSET 251

          or use  the  value appropriate  for  the higher  modulator  tone.
          Next, enter

                    cmd:CALIBRA

          Now  press the  K key.   Either  the CON  or the  STA LED  should
          illuminate.  Tap the space bar until the STA LED glows.

          Slowly  rotate the adjustment screw of  trimpot R77 CW, following
          the  instructions above for setting R78.  Continue the adjustment
          until both the STA and CON LEDs glow steadily.

          When both LEDs  are steadily illuminated, press the  Q key.  Both
          LEDs  should  extinguish  and  the  command  mode  prompt  should
          reappear.  Remove the jumpers at JMP9 pins 1 & 6 and at JMP4.






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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Demodulator Adjustment

          NOTE:    Do  not  remove  the  jumper  at  JMP8  for  demodulator
          calibration!

          To calibrate the  PLL demodulator, preset R79  20 turns clockwise
          (CW) or until  you hear the element "click" at  full CW rotation.
          Place a jumper across JMP9 pins 3  and 4 (the lowest two pins  --
          these are  the two  pins nearest  the  silkscreen legend  "C43").
          Install  a push-on jumper at JMP4 (to disable the transmitter PTT
          watchdog  timer)  and  another  at  JMP7  (to  establish  "analog
          loopback").  Enter

                    cmd:RXCAL

          at the computer or terminal keyboard.

          Now press the K key.  The STA LED should illuminate.

          Slowly rotate the adjustment screw of R79 CCW until  both the STA
          and  CON  LEDs  glow.   This  is a  very  difficult  condition to
          achieve,  partly because  the  indicator is  quite sensitive  and
          partly because the LEDs  lag the adjustment by  a second or  two.
          However, if you establish  the position of the trimpot  where the
          LEDs toggle  and leave R79 set  to within about 1/4  turn of that
          position there will be no degradtion in performance.

          Type Q and note that the  command mode prompt reappears.   Remove
          the  jumpers at  JMP4, JMP7 and  JMP9.   Your TNC 2  modem is now
          calibrated to the tones you have selected.

          Other Considerations

          If  you are operating  at a data  rate other than  1200 baud, the
          loop timing  components on your demodulator will  not be optimum.
          The  table  below lists  the component  values  for the  two most
          common FSK pairs as well as CALSET parameters.














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          Tucson Amateur Packet Radio                   TNC 2 System Manual

                         Modem Calibration Parameters.

                     Data rate          1200 baud 300 baud
                     Shift              800 Hz    200 Hz
                     Center Freq        1700 Hz   1700 Hz
                     Upper Freq         2100 Hz   1800 Hz
                     Lower Freq         1300 Hz   1600 Hz

                     C54           2200 pF   0.01 uF
                     R93           47.5 k         226 k

                     CALSET Parameters

                     High Tone (R77)    251       293
                     Low Tone  (R78)    405       329

          NOTE:  Components   used  for  R93  and  C54   should  have  tem-
          perature-stable characteristics.

          Finally, it is best to match the IF bandwidth of your receiver to
          the data  rate you will  operate.  For  300 baud HF  operation, a
          filter of  about 500 Hz bandwidth is optimum; any CW filter wider
          than this should be better than an SSB bandwidth filter!




























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          Chapter 6  TAPR TNC 2 COMMANDS



          This  chapter serves as a complete reference to all TNC commands.
          Commands  are used  to  control the  many  variable values  which
          affect your TNC's  operation, as  well as causing  it to  perform
          specific actions, such as connecting to another station to  start
          a QSO.  You can enter a command to your TNC  whenever you see the
          command-mode prompt:

               cmd:

          You will change parameters  and issue instructions to the  TNC by
          typing   commands  composed   of  English-like   words  or   word
          abbreviations, which are called keywords, and variables which are
          numbers or strings  of characters chosen by  the user.   You will
          probably never change some  of these parameters; however, one  of
          TAPR's goals is to  allow each user maximum flexibility  to adapt
          the TNC to his environment.


          Entering Commands

          You may use  either upper  case (capital letters)  or lower  case
          (small letters)  when you enter commands.   In order to have your
          TNC accept a command line, you  must finish the line with a <CR>,
          or carriage return character.  This won't be mentioned explicitly
          in the  examples below.  Before  you type the final  <CR> of your
          command,  you can  correct  typing mistakes  or  cancel the  line
          completely.    See  Chapter 4  for  a  discussion  of input  line
          editing.

          This chapter will use  UPPER CASE for commands and lower case for
          explanatory  text.  In examples  showing input typed  by the user
          together with the responses of the TNC, the  user's input will be
          shown in bold face.

          Whenever the TNC accepts a command which changes a value, it will
          display the previous value.  For example, if you type

               XFLOW OFF

          you might see the display

               XFLOW was ON

          This reminds you  of what you  have done, and indicates  that the
          value has been successfully changed.


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          If  you type something your TNC can't  understand you will get an
          error message.  If you type an unrecognized command, you will see
          the message  ?EH.   If you  get a command  name correct,  but the
          arguments are  wrong, you will see the  message ?BAD.  A complete
          list  of error messages appears at the  end of this chapter.  For
          example,

               cmd:ASDFASDF        || This isn't a command.
               ?EH
               cmd:BEACON E        || A parameter was left out.
               ?BAD


          Command List

          The commands  are listed  alphabetically, and each  command entry
          contains several sections, as follows.

          COMMAND NAME

          The boldface command name at the top of the entry is the word you
          will type  in order to have  your TNC execute this  command.  The
          command name is printed with some letters underlined.  These let-
          ters form the  minimum abbreviation  that you may  use and  still
          have your TNC understand your  command.  Of course, you may  type
          out  the entire command word, or any abbreviation longer than the
          minimum abbreviation, if you like.

          For example, the command MYCALL may be specified by simply typing
          MY.     The  abbreviation  M  is  not  sufficient  (and  will  be
          interpreted  as a different command), but MY, MYC, MYCA, MYCAL or
          MYCALL are all acceptable.

          If the command requires parameters, they will  be indicated after
          the command name.

          Default

          For  commands that  set values,  your TNC  assumes a  "most often
          used" or default condition.   The defaults are the  values stored
          in  EPROM  which are  loaded into  RAM when  the system  is first
          powered  up, or  when  you give  the  RESET command.    Immediate
          commands perform  actions rather  than setting values,  and don't
          have defaults.

          Parameters

          There  are several types of parameters.  Some parameters can have
          one of only  two values, such as  ON and OFF or  EVERY and AFTER.
          If  a parameter must be one of  two values, the choices are shown

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          separated by a vertical  bar.  You may use YES instead  of ON and
          NO instead of OFF.


          A parameter designated as n is a numeric value.  These values may
          be entered  as ordinary  decimal numbers,  or as  hexadecimal, or
          "hex",   numbers by preceding the  number with a $  symbol.  When
          the TNC shows some  of these numeric parameters (those  which set
          special characters), they will be given in hex.   The "digits" of
          a hex number  represent powers of 16, analogous  to the powers of
          10 represented  by a decimal number.   The numbers  10 through 15
          are denoted by the hex digits A through F.  For example,

               $1B = 1*16 + 11 = 27
               $120 = 1*16*16 + 2*16 + 0 = 288

          A  parameter designated as text,  such as the  argument to CTEXT,
          may be entered  in upper or lower case, and  may include numbers,
          spaces, and punctuation.   The text is accepted exactly  as typed
          by the user.

          Several commands  require callsigns  as parameters.   While these
          parameters are normally  Amateur call signs, they may actually be
          any  collection of  numbers and  at least  one letter  up to  six
          characters;  they  are  used  to identify  stations  sending  and
          receiving   packets.    A   callsign  may   additionally  include
          sub-station ID  (SSID), which is  a decimal number  from 0 to  15
          used to distinguish two or more stations on the air with the same
          Amateur  call (such as a base station  and a repeater).  The call
          sign and SSID are entered and displayed as call-n, e.g., K0PFX-3.
          If the SSID is  not entered, it is set  to 0, and SSIDs of  0 are
          not displayed by the TNC.

          Some commands have parameters which are actually  lists of items.
          For example,  you may specify  as many  as eight callsigns  to be
          selectively monitored  with the command  LCALLS.  The  second and
          later items in  the list are  optional, and you may  separate the
          list items with blank spaces or with commas.


               BEACON EVERY|AFTER n

          means  that the command BEACON requires an argument which must be
          either EVERY or AFTER (abbreviated to E or A), and  an argument n
          which the user may choose from  a range of values.  An acceptable
          command might be BEACON E 2.

               CONNECT call1 [VIA call2[,call3...,call9]]



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          means  that  the command  CONNECT  requires  a callsign  argument
          call1.  You may optionally include the keyword VIA, followed by a
          list  of  one  to eight  callsigns,  call2  through  call9.   The
          callsigns in the list,  if included, must be separated  by commas
          (as shown), or by blank spaces.  An acceptable command might be C
          N2WX V AD7I WB9FLW.

          You  can  see the  current value  of  the command's  arguments by
          typing  the command name by  itself, without any  arguments.  For
          example,

               cmd:CONOK Y         || Sets the value to YES (ON).
               CONOK was OFF  || Displays previous value.
               cmd:CONOK           || Command with no arguments
               CONOK ON            || Displays present value.

          A special command, DISPLAY, allows you  to see the values of  all
          parameters or groups of related parameters.

          Remarks

          This  section describes the  command's action and  the meaning of
          each argument.  Examples  may be included of situations  in which
          the command might be used.



























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          8BITCONV ON|OFF                                      Default: OFF
                                                           Display Group: A

          Parameters:

               ON   The high-order bit is not stripped in Converse Mode.

               OFF  The high-order bit is stripped in Converse Mode.

          This command enables transmission of 8-bit data in Converse Mode.
          If  8BITCONV is  OFF, the  high-order bit  (bit 7)  of characters
          received  from the terminal is removed  before the characters are
          transmitted  in  a packet.    The  standard  ASCII character  set
          requires only 7 bits,  and the final bit is used as  a parity bit
          or  ignored.  Setting bit  7 in text  characters transmitted over
          the air may cause confusion at the other end.

          If  you need  to  transmit 8-bit  data, but  don't  want all  the
          features  of Transparent  Mode, you  should set  8BITCONV ON  and
          AWLEN 8.  This may  be desirable, for example, if you are using a
          special non-ASCII character set.

          Bit 7 is always  removed in Command Mode, since  commands require
          only the standard 7-bit ASCII character set.


          ACKPRIOR ON|OFF                                       Default: ON
                                                           Display Group: L

          Parameters:

               ON   Enables Prioritized acknowledgments.

               OFF  Acknowledgments  have the  same priority  as any  other
                    frames on the channel.

          When ACKPRIOR is  ON, acknowledgments have priority.   This means
          that is your TNC receives a frame that it must acknowledge (ACK),
          it will  immediately send the  ACK if the  channel is clear.   If
          other stations are running with ACKPRIOR ON, they will not access
          the channel until you have had a  chance to send the ACK, even if
          they cannot hear your transmissions.

          When OFF, acknowledgments are queued up for transmission the same
          as any other frame.






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          ACKTIME n                                             Default: 14
                                                           Display Group: T

          Parameters:

               n         0-250 in 10 mSec increments.

          ACKTIME specifies the time required to send an RR or RNR response
          frame (an  acknowledgment) to an  I frame at the  radio port data
          rate.   This corresponds to  about 510  mSec at 1200  bps with  8
          digipeaters and about 140  mSec at 1200 bps with  no digipeaters.
          The default of 140 mSec (ACKT 14) allows for no digipeaters.


          ANSWRQRA  ON|OFF                                      Default: ON

          Setting ANSWRQRA  to OFF  disables the TNC's  ping-response func-
          tion.   When the parameter  is set ON,  the TNC responds  to non-
          digipeated  UI frames addressed to  QRA, within 1  to 16 seconds,
          with an empty ID packet.  TNC-2 ignores QRA packets when ANSWRQRA
          is off.


          AUTOLF ON|OFF                                         Default: ON
                                                           Display Group: A

          Parameters:

               ON   A  linefeed character  (<LF>) is  sent to  the terminal
                    after each carriage return character (<CR>).

               OFF  A <LF> is not sent to the terminal after each <CR>.

          AUTOLF  controls  the  display   of  carriage  return  characters
          received in packets as well as echoing those that are typed in.

          If the  TNC's sign-on message lines appear  to be typed over each
          other,  you should set AUTOLF  ON.  If  the TNC's sign-on message
          appears to be double-spaced, you should  set AUTOLF OFF.  If  the
          TNC's  sign-on  message appears  to  be  single-spaced, you  have
          AUTOLF set correctly.

          This command only affects what is displayed, not the data sent in
          packets.   If  you want  to add  linefeed characters  to outgoing
          packets, use the command LFADD.






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          AWLEN n                                                Default: 7
                                                           Display Group: A

          Parameters:

               n         7  - 8,  specifying the  number of  data bits  per
                         word.

          This value defines the word length used by the serial IO terminal
          port.

          For  most  packet  operations, including  conversation,  bulletin
          board  operation, and transmission of ASCII files, you should set
          AWLEN  7.  If 8  bit words are transmitted to  the TNC in Command
          Mode  or  Converse Mode,  the  eighth  bit is  normally  removed,
          leaving a standard ASCII character, regardless of  the setting of
          AWLEN.

          To transmit and receive packets retaining all 8 data bits of each
          character, as  you need to  do if  you send  executable files  or
          other special data, you should use Transparent Mode and set AWLEN
          8.   Alternatively, you can use Converse Mode and set AWLEN 8 and
          8BITCONV  ON (however,  the data  you then  send must  handle the
          Converse Mode special characters with the PASS prefix).


          AX25L2V2 ON|OFF                                       Default: ON
                                                           Display Group: L

          Parameters:

               ON   The TNC will use AX.25 Level 2 Version 2.0 protocol.

               OFF  The TNC will use AX.25 Level 2 Version 1.0 protocol.

          Some  implementations of  the earlier  version of  AX.25 protocol
          (e.g., TAPR's  TNC 1  running TAPR  3.x firmware)  won't properly
          digipeat  version  2.0 AX.25  packets.   This  command  exists to
          provide compatibility with these  other TNCs until their software
          has been updated.

          In addition,  some HF packet  operators prefer AX.25  Version 1.0
          protocol due to its reduced overhead during retries.








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          AXDELAY n                                              Default: 0
                                                           Display Group: T

          Parameters:

               n         0 - 180, specifying the voice repeater keyup delay
                         in 10 ms intervals.

          AXDELAY  specifies a  period  of time  the  TNC  is to  wait,  in
          addition to the  normal delay  set by TXDELAY,  after keying  the
          transmitter and before data is  sent.  This feature will  be used
          by groups using a  standard "voice" repeater to extend  the range
          of  the  local area  network.    Repeaters  with slow  mechanical
          relays, split  sites, or other circuits  which delay transmission
          for some time after the RF carrier is present require some amount
          of time to get RF on the air.

          If you  are using  a repeater  that hasn't  been used  for packet
          operations before, you will  have to experiment to find  the best
          value  for n.    If other  packet  stations have  been using  the
          repeater, check with them  for the proper setting.   This command
          acts in conjunction with AXHANG.

          Note that  the TAPR TNC 1  and other TNCs using  the same version
          3.x firmware interpret n in  120 ms intervals.  The value  set by
          AXDELAY on TNC 2 will thus be 12 times  the value used by a TNC 1
          user to give the same delay time.
























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          AXHANG n                                               Default: 0
                                                           Display Group: T

          Parameters:

               n         0 - 20, specifying the voice repeater hang time in
                         100 ms intervals.

          This value can  be used  to increase channel  efficiency when  an
          audio repeater with a hang time greater than 100 ms is used.  For
          a repeater with a long hang time, it is not necessary to wait for
          the  repeater keyup  delay  after keying  the transmitter  if the
          repeater is  still transmitting.  If  the TNC has heard  a packet
          sent within the hang period,  it will not add the repeater  keyup
          delay (AXDELAY) to the keyup time.

          If  you are  using a  repeater that  hasn't been used  for packet
          operations before, you will  have to experiment to find  the best
          value  for  n.   If  other packet  stations have  been  using the
          repeater, check with them for the proper setting.

          Note that  the TAPR TNC 1  and other TNCs using  the same version
          3.x firmware interpret n in 120 ms intervals.  The  value you set
          on TNC 2 for  AXHANG will thus be 6/5  the value used by a  TNC 1
          user for the same hang  time (when converting, round down to  the
          nearest integer).

























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          BBSMSGS ON|OFF                                       Default: OFF
                                                           Display Group: A

          This  command controls how  the TNC displays  certain messages in
          COMMAND and CONVERSE  modes.  The messages affected are described
          below:


          MESSAGE             EFFECT WHEN BBSMSGS ON

          *** CONNECTED to  xxxx   -  A newline added preceding "***"
          *** DISCONNECTED         -         "            "
          *** retry limit exceeded -         "            "
          *** xxxx Busy            -         "            "
          *** FRMR sent            -         "            "
          *** FRMR rcvd            -         "            "

          *** Connect request: xxxx     -   This message is omitted


          The BBSMSGS command is primarily useful for host  operation, such
          as with  W0RLI and  similar bulletin board  systems that  require
          link status messages to begin in the first output column.

          The connect request message is omitted during BBSMSGS mode.  This
          should be most useful for preventing corruption of messages  when
          forwarding with small frames.
























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          BEACON EVERY|AFTER n                             Default: EVERY 0
                                                           Display Group: I

          Parameters:

               EVERY     Send beacon at regular intervals.

               AFTER     Send beacon once after the specified time interval
                         with no packet activity.

               n         0  - 250,  specifying beacon  timing in  10 second
                         intervals.  A value of 0 disables the beacon.

          This  command enables beacon sending  and causes the first beacon
          frame to be  transmitted.  A  beacon frame consists  of the  text
          specified by BTEXT in a packet addressed to "BEACON" and sent via
          the digipeat addresses specified by the UNPROTO command, if any.

          If the keyword EVERY is specified, a  beacon packet is sent every
          n*10 seconds.   This mode  might be used to  transmit packets for
          testing purposes.

          If  AFTER is specified, a beacon is  sent only after n*10 seconds
          have passed with no packet activity.  In this case, the beacon is
          sent only once until further activity is detected.  This mode can
          be used to send  announcements or test messages only  when packet
          stations  are on the air.  If you choose n properly you can avoid
          cluttering a busy channel with unnecessary transmissions.

          Beacon frames from other TNCs can be monitored by setting MONITOR
          ON.




















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          BKONDEL ON|OFF                                        Default: ON
                                                           Display Group: C

          Parameters:

               ON   The sequence <BACKSPACE>  <SPACE> <BACKSPACE> is echoed
                    when a character is deleted from the input line.

               OFF  The  <BACKSLASH>  character   (\)  is  echoed   when  a
                    character is deleted.

          This command determines the way the display is updated to reflect
          a character deletion in Command Mode or Converse  Mode.

          The <BACKSPACE> <SPACE> <BACKSPACE> sequence will properly update
          the  screen of  a video  display.   If you  have a  video display
          terminal or computer, you should set BKONDEL ON.

          The  <BACKSPACE>  <SPACE>  <BACKSPACE>  sequence  on  a  printing
          terminal  would  result  in  overtyped  text.    If  you  have  a
          paper-output display, or if your terminal does not respond to the
          <BACKSPACE>  character (<CTRL-H>),  you should  set BKONDEL  OFF.
          The  TNC will type a  <BACKSLASH> for each  character you delete.
          You  can  display   the  corrected  input  line   by  typing  the
          redisplay-line character, which is set by the command REDISPLA.

          NOTE:  BKONDEL is only active in COMMAND and CONVERSE modes.
























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          BTEXT text                                            Default: ""
                                                           Display Group: I

          Parameters:

               text Any  combination  of characters  and  spaces,  up to  a
                    maximum length of 120 characters.

          BTEXT  specifies  the content  of the  data  portion of  a beacon
          packet.  The  default text is an empty  string, i.e., no message.
          Beacon  packets  are discussed  in more  detail under  the BEACON
          command.

          You  can send multiple-line messages  in your beacon by including
          carriage  return  (<CR>)  characters  in  the  text.    The  <CR>
          character can be included  by preceding it with the  pass charac-
          ter.  The  pass character is  set by  the PASS command.   If  you
          enter  a text string longer than 120 characters, an error message
          will appear and the command will be ignored.

          For example, a Bulletin  Board program might set the  beacon text
          to a message like this, updating the text after each connection:

               Mailbox on line.  Messages for WB9FLW, AD7I, K9NG.

          To clear the BTEXT text without issuing the RESET command,  use a
          % or & character as the first character in the text.


          The BTEXT text is stored in battery-backed RAM.





















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          BUDLIST ON|OFF                                       Default: OFF
                                                           Display Group: M

          Parameters:

               ON   Ignore frames from stations which are not in the LCALLS
                    list.

               OFF  Ignore  frame from  stations  which are  in the  LCALLS
                    list.

          BUDLIST works in conjunction with the command LCALLS,  which sets
          up  a callsign list.  These commands determine which packets will
          be displayed when  you have  set MONITOR ON.   BUDLIST  specifies
          whether the callsigns in the list are the ones you want to ignore
          or, alternatively, are the only ones you want to listen to.

          If you want  to listen only for packets from  a limited list, you
          should enter this list with  LCALLS and set BUDLIST ON.   You can
          use this feature, for example, to have your TNC "keep an ear out"
          for a particular station while you converse with someone else.

          If you want  to ignore  packets from a  limited list, you  should
          list the callsigns to ignore in  LCALLS and set BUDLIST OFF.  For
          example,  if  there is  a bulletin  board  on frequency,  you can
          ignore it while monitoring other conversations.


          CALIBRA
                                                        Display Group: NONE

          CALIBRA  is an immediate command, and is used to transfer control
          to the modem  calibration routine.  Calibration  may be performed
          at any time without altering the current link state.

          Briefly, the commands available in the calibration routine are:

                 <SPACE> Switch the transmit audio to the other tone.
                    D         Alternate between the two transmit tones at a
                              rate determined by the radio port data rate.
                    K         Toggle PTT line on/off.
                    Q         Quit calibration routine.

          Calibration  of  the  modem  tones  is  described  in  the  modem
          calibration  section of Chapter 5.  Adjustment of the tone levels
          using CALIBRA is described in Chapter 3.  See also RXCAL.





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          CALSET n                                            Default: None
                                                           Display Group: T

          Parameters:

               n         0 - 65535, specifying the count setting for use by
                         the calibration routine.

          The  number  to  be specified  by  CALSET  is  determined by  the
          frequency f to be calibrated as follows.

                    n = (525,000 / f) + 1         (modulator tones)
                    n = (262,500 / f) + 1         (demodulator tones)

          Round n to  the nearest integer.   To calibrate the  modem tones,
          you  will set n for the desired frequency using CALSET, enter the
          calibration routine  with CALIBRA, and adjust  the tone following
          the instructions in Chapter 5.   To calibrate the next tone, exit
          the calibration routine and set n for the next frequency.

          See also RXCAL.






























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          CANLINE n                                   Default: $18 <CTRL-X>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This command  is used  to  change the  cancel-line input  editing
          command character.   The parameter  n is the  ASCII code  for the
          character you want to type in order to cancel an input line.  You
          can enter the code in either hex or decimal.

          For example, to change the cancel-line character to <CTRL-U>, you
          would set CANLINE $15 or CANLINE 21.

          If  you cancel an  input line in  Command Mode, the  line will be
          terminated with a <BACKSLASH>  character, and you will see  a new
          cmd: prompt.  If you cancel a line in Converse Mode, you will see
          only  the <BACKSLASH> and  a new line.   You can  cancel only the
          line you are currently typing.  Once a <CR> has been entered, you
          can  not cancel that input line  using the cancel-line character.
          Note  that  if  your  send-packet  character  is  not  <CR>,  the
          cancel-line  character  will cancel  only  the  last  line  of  a
          multi-line packet.  To  cancel the entire packet, use  the CANPAC
          character.

          Line  cancellation, like  all  other input  editing features,  is
          disabled in Transparent Mode.























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          CANPAC n                                    Default: $19 <CTRL-Y>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          CANPAC is used to change the cancel-packet input editing  command
          character.   The parameter n is  the ASCII code for the character
          you want  to type in  order to cancel an  input packet.   You can
          enter the code in either hex or decimal.

          If  you cancel  a  packet  in Converse  Mode,  the  line will  be
          terminated with a <BACKSLASH> character and a new  line.  You can
          only cancel the packet that is currently being entered.  Once you
          have  typed  the send-packet  character,  or  waited PACTIME  (if
          CPACTIME enabled), the  packet can not be canceled even if it has
          not been transmitted.

          Packet  cancellation,  like  other  input  editing  features,  is
          disabled in Transparent Mode.

          Cancel Display Output

          The  cancel-packet  character  also functions  to  cancel display
          output in Command Mode.  If you are in  Command Mode and type the
          cancel-packet character,  any characters  that would be  typed on
          the screen  (except echoed characters)  are "thrown away"  by the
          TNC.  Typing the  cancel-output character a second  time restores
          normal output.  To  see how this works, try typing  DISPLAY, then
          type a  <CTRL-Y>.  The command list display will stop.  You won't
          see any  response from  the TNC to  commands.   Now type  another
          <CTRL-Y>, and  type DISPLAY again to see that the display is back
          to normal.

          You can  use the cancel-display  feature if you  inadvertently do
          something that causes the TNC to generate large amounts of output
          to  the terminal, such as  giving the DISPLAY  command or setting
          TRACE ON.   If you are  in Converse Mode or  Transparent Mode and
          want to cancel display output, you  must exit to Command Mode and
          then type the cancel-packet character.










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          CBELL ON|OFF                                         Default: OFF
                                                           Display Group: I

          Parameters:

               ON   Connect bell enabled.

               OFF  Connect bell disabled.

          This  command  is used  to control  whether  an ASCII  $07 (BELL)
          character is sent as part of the connected message.

          When set ON, the bell character immediately precedes the asterisk
          portion of the connected message, e.g.:

               <BELL>*** Connected to: <callsign>



































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          CHECK n                                               Default: 12
                                                           Display Group: T

          Parameters:

               n         0 -  250, specifying the  check time in  10 second
                         intervals.  A value of 0 disables this feature.

          This  command sets a connection  time-out.  If  a link connection
          exists  between  your TNC  and  another  station, and  the  other
          station  "disappears," your  TNC  could remain  in the  connected
          state  indefinitely, refusing  connections  from other  stations.
          This  might  happen if  propagation  changes  unexpectedly or  an
          intermediate  digipeater  station is  turned  off.   In  order to
          prevent this  sort of lockup,  the TNC will  try to clean  up the
          link if  the  specified time  elapses without  any packets  being
          heard from the  other TNC.  The operation of this feature depends
          on the setting of AX25L2V2.

          If  AX25L2V2 is ON, the TNC will  send a "check packet" to verify
          the presence of  the other station if no  packets have been heard
          from  it for n*10 seconds.   This frame  contains no information,
          but is interpreted by  the receiving station's TNC as  an inquiry
          as to  whether it is  still connected.   If the receiving  TNC is
          still connected, it sends an appropriate response packet.  If the
          TNC initiating the inquiry does not hear a response after RETRY+1
          attempts, it  commences a disconnect sequence, as if the DISCONNE
          command had been given.

          If AX25L2V2 is  OFF and the other station has  not been heard for
          n*10 seconds, the TNC will not attempt an inquiry,  but will send
          a  disconnect  packet,  just as  if  you  had  typed the  command
          DISCONNE, unless CHECKV1 is OFF.  See also CHECKV1. 


















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          CHECKV1 ON|OFF                                       Default: OFF
                                                           Display Group: T

          Parameters:

               ON   Enables  CHECKtime  (T3)  when running  AX.25  Level  2
                    Version 1.0 protocol.  This will result in an automatic
                    disconnect when packets haven't flowed between this TNC
                    and the remote TNC for CHECKtime.  See CHECK, above.

               OFF  Disables  the  CHECKtime  timer (T3)  and  requires the
                    operator to initiate a disconnect sequence.  This is in
                    accordance with AX.25 Level 2 Version 1.0 procedures.

          When ON, the CHECK (T3) timer is used to automatically disconnect
          an AX.25  Level 2 Version  1.0 link when  data hasn't flowed  for
          CHECK  time.    Note  that  T3 is  not  defined  for  Version 1.0
          operation.  See CHECK, above.

          When OFF, T3 is ignored and normal Version 1.0 procedures apply.

          NOTE:    Many  operators   prefer  using  Version  1.0  protocol,
          especially  on marginal or noisy links in order to eliminate some
          of the overhead of AX.25 Level 2 Version 2.0 protocol.


          CLKADJ n                                               Default: 0
                                                           Display Group: T

          Parameters:

               n         0 - 65535, specifying  the correction factor to be
                         applied to the real-time clock routine.

          A  value of "0" is a special  case and means no correction factor
          will be  applied.  If the  value of CLKADJ is  non-zero, then the
          correction factor is calculated as:

                                                                
             relative clock speed in % =  100 - ( 9.16667 *  1/n)
                                                                

          The real-time clock routine is used to keep track of year, month,
          day, hour, minute and second as specified in the DAYTIME command.
          It should be noted that the real-time clock is not intended to be
          your  ham-shack reference  clock, but  is useful  for approximate
          time stamping information.




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          CMDTIME n                                              Default: 1
                                                           Display Group: T

          Parameters:

               n         0  -  250,  specifying Transparent  Mode  time-out
                         value  in 1 second intervals.   If n  is zero, the
                         only exit from Transparent Mode is to send a BREAK
                         signal or interrupt power to the TNC.

          This  command sets the Transparent Mode time-out value.  In order
          to  allow escape  to  Command Mode  from  Transparent Mode  while
          permitting any  character to be sent  as data, a guard  time of n
          seconds is set up.

          The same Command Mode entry character used for exit from Converse
          Mode  is  used to  exit Transparent  Mode,  but the  procedure is
          different.  (The Command Mode entry character is set by COMMAND.)
          Three Command Mode entry  characters must be entered less  than n
          seconds apart, with no intervening characters, after a delay of n
          seconds  since the  last characters  were typed.   After  a final
          delay of  n seconds, the TNC will exit Transparent Mode and enter
          Command Mode.  You should then see the prompt

               cmd:

          The diagram below illustrates this timing.

          last           first       second      third         TNC
          terminal       command     command     command       now in 
          input          mode        mode        mode          Command
          |              entry       entry       entry         Mode
          |              character   character   character     |
          |              |           |           |             |
          |              |           |           |             |
          |<---longer--->|<-shorter->|<-shorter->|<-----n----->|
               than n       than n      than n














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          CMSG ON|OFF                                          Default: OFF
                                                           Display Group: I

          Parameters:

               ON   The CTEXT message is  sent as the first packet  after a
                    connection is established.

               OFF  The CTEXT message is not sent.

          CMSG  enables  automatic  sending of  the  message  set by  CTEXT
          whenever your TNC accepts a connect request from another TNC.  

          For  example, if you have  left your station  running even though
          you don't want to operate just now, you might want to set CMSG ON
          to let  people know that you can't talk when they connect to your
          TNC.  When you are ready to operate, you would set CMSG OFF.


          CMSGDISC ON|OFF                                      Default: OFF
                                                           Display Group: I

          Parameters:

               ON   Automatic disconnect enabled.

               OFF  Automatic disconnect disabled.

          This command controls whether the TNC  will initiate a disconnect
          sequence after it is connected to.

          If CMSG is OFF, or CTEXT has no connected text, the TNC initiates
          a   disconnect   immediately   upon  receiving   information   or
          acknowledgment frames from the other station.

          If CMSG is ON and  CTEXT contains some text information, the  TNC
          initiates a  disconnect after the packet  containing connect text
          (CTEXT) is acknowledged.

          This  command may be useful to bulletin board operators or others
          with a need  to send a  short message,  confirm its receipt,  and
          disconnect.

          NOTE:  Use this  command with care -  If you find you're  able to
          receive connects,  yet never get data, it's possible CMSGDISC has
          been left  on. It's also possible  is that RS-232 DCD  is holding
          the  terminal off --  see Chapter 5 for  details on hardware flow
          control.



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          COMMAND n                                   Default: $03 <CTRL-C>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This  command is used to change the Command Mode entry character.
          You can enter the code in either hex or decimal.

          Command Mode is entered from Converse Mode when this character is
          typed.  If you  type the Command Mode  entry character while  you
          are already  in Command Mode,  nothing will  happen.  To  see how
          this  works, enter Converse Mode by typing CONVERS.  Anything you
          type will become packet data.  Now type a <CTRL-C>.  You will see
          the Command  Mode prompt,  indicating successful exit  to Command
          Mode.  The display might look like this:

               cmd:CONVERS
               Hello World!  I'm on the air on packet radio!
               [enter <CTRL-C>]
               cmd:

          See the  entry under CMDTIME  for information  on how to  use the
          Command Mode entry character to escape from Transparent Mode.


























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          CONMODE CONVERS|TRANS                            Default: CONVERS
                                                           Display Group: L

          Parameters:

               CONVERS   Sets  automatic  entry  to Converse  Mode  when  a
                         connection is established.

               TRANS          Sets automatic entry to Transparent Mode when
                              a connection is established.

          CONMODE controls which  mode the  TNC will be  placed in after  a
          connection.   The  connection may  result  either from  a connect
          request received over the air or a connect initiated by a CONNECT
          command  that  you issue.   For  most  operations, you  would set
          CONMODE to CONVERS.   However, if you are using  Transparent Mode
          for  a bulletin board program, for example, you would set CONMODE
          to  TRANS so  that the  correct mode  will be  entered when  your
          bulletin board receives a connect request.

          If you initiate a connection with the CONNECT command, the timing
          of the entry into  Converse or Transparent Mode is  determined by
          NEWMODE.

          If  the TNC is  already in Converse or  Transparent Mode when the
          connection is completed,  the mode will  not be changed.   If you
          have  typed part  of  a  command  line  when  the  connection  is
          completed, the mode change will not take place until you complete
          the  command or cancel the line.   This prevents the last part of
          your command from inadvertently being sent as a packet.





















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          CONNECT call1 [VIA call2[,call3...,call9]]
                                                        Display Group: NONE

          Parameters:

               call1     Callsign of TNC to be connected to.

               call2     Optional callsign of TNC to be digipeated through.
                         As   many  as  eight  digipeat  addresses  can  be
                         specified.

          The  part   of  the  command   line  in  brackets,   VIA  call2[,
          call3...,call9]   is  optional.     The   double-bracketed  text,
          ,call3...,call9, is also optional, but would only be used if  VIA
          call2 is present.  The brackets are not typed.

          Each callsign may include an optional sub-station ID specified as
          -n immediately following the  callsign.  The digipeat fields  are
          specified  in  the order  in  which you  want them  to  relay the
          packets to the destination, call1.

          CONNECT  is an immediate command.  It initiates a connect request
          to  TNC call1, optionally through digipeaters.  If NEWMODE is ON,
          the TNC will immediately enter Converse Mode or Transparent Mode,
          as specified  by the command CONMODE.  If NEWMODE is OFF, the TNC
          will enter Converse Mode or Transparent Mode when the  connection
          is successfully completed.

          An error message is returned if the TNC is in  a connected state,
          or  is  already  attempting to  connect  or  disconnect.   If  no
          response  to  the connect  request  occurs  after  the number  of
          attempts specified by RETRY, the command is aborted and a message
          is typed.  The TNC returns to Command Mode  if NEWMODE is ON.  If
          NEWMODE is OFF, the mode does not change, i.e. the TNC remains in
          Command Mode.

          For example, to connect to WA7GXD using N0ADI-1 (who is near your
          QTH) and WD0ETZ (who is near GXD's QTH) as digipeaters, you would
          type

               CONNECT WA7GXD VIA N0ADI-1,WD0ETZ

          Packets  coming back from  WA7GXD access  the digipeaters  in the
          opposite order.  Thus, packets from WA7GXD will first be repeated
          by WD0ETZ, then by N0ADI-1.






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          CONOK ON|OFF                                          Default: ON
                                                           Display Group: L

          Parameters:

               ON   Connect requests from other TNCs will be accepted.

               OFF  Connect requests from other TNCs will be rejected.

          This  command determines  the  action taken  by  the TNC  when  a
          connect request for it is received though the radio.  If CONOK is
          ON,  the  request  will  be acknowledged,  the  standard  connect
          message will  be typed  and either Converse  or Transparent  Mode
          will be entered, depending on the setting of CONMODE.

          If  CONOK is OFF and the TNC is  not in Transparent Mode, the TNC
          will  notify  you  of  the  connect  attempt  with  the following
          message.

               connect request: <call>

          The  callsign  of the  station  trying  to  connect will  replace
          <call>.

          The TNC  will also issue  a DM  packet, or "busy  signal" to  the
          requesting  station.   The user  may then  issue his  own connect
          command.   If  your TNC  receives a  DM packet  in response  to a
          connect request, it will type the message

               *** <call> station busy

          with the callsign of the station that sent the DM packet in place
          of <call>.

          For  example, if  you want  to leave  your station  running as  a
          digipeater  you might set  CONOK OFF  until you  are ready  for a
          conversation.  If you get a connect request in the  meantime, you
          can change your mind.  Stations attempting to connect to your TNC
          will be able to see that the station is  up but not available for
          connection (it might still be useful as a digipeater).











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          CONPERM ON|OFF                                       Default: OFF
                                                           Display Group: L

          Parameters:

               ON   The current  connection on the current  stream will not
                    be allowed to enter the disconnected state.

               OFF  The current stream may be connected to and disconnected
                    from other stations.

          This command, when switched ON, forces the TNC to always maintain
          the current  connection, even  when frames to  the other  station
          exceed  RETRY attempts  to get  an acknowledgment.    RESTART and
          power off/on cycling will not affect this connected state.

          This command only takes effect when a connection is  established.
          It functions  on a  stream-by-stream basis when  multiple connec-
          tions are allowed.

          It is useful for  certain networking applications, meteor scatter
          and other  noisy, less-reliable links, while  still allowing con-
          nections on other streams  to operate normally (automatic discon-
          nect based on RETRY, etc.).


          CONSTAMP ON|OFF                                      Default: OFF
                                                           Display Group: M

          Parameters:

               ON   Connect status messages are time stamped.

               OFF  Connect status messages are not time stamped.

          This  command  enables  time  stamping of  ***  CONNECTED  status
          messages.   The date and  time information is  then available for
          use by  Bulletin Board  programs or other  computer applications.
          The date and  time must be set  initially by the  DAYTIME command
          before time stamping will  occur.  The date format  is determined
          by the DAYUSA command.

          For example,  if CONSTAMP is ON,  DAYUSA is ON, and  the date and
          time have been set, a connect message might appear as follows.

               *** CONNECTED to N2WX [05/28/85 16:28:31]





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          CONVERS
                                                        Display Group: NONE

          CONVERS is  an immediate command, and will  cause the TNC to exit
          from Command Mode into  Converse Mode.  Any link  connections are
          not  affected.   Once in  Converse Mode,  everything you  type is
          packetized  and transmitted over  the radio.   Typing the Command
          Mode entry character  returns the TNC to  Command Mode.  See  the
          discussions of Converse Mode in Chapters 4 and 5.

          NOTE:   The letter "K" may be  used to more quickly enter CONVERS
          mode.


          CPACTIME ON|OFF                                      Default: OFF
                                                           Display Group: T

          Parameters:

               ON   Packet time-out is used in Converse Mode.

               OFF  Packet time-out is not used in Converse Mode.

          This command enables the periodic automatic sending of packets in
          Converse   Mode.    This   feature  may  be   used  for  computer
          communications, such  as Bulletin Board operation,  when the full
          Transparent Mode features are not desired.

          If  CPACTIME is  ON,  characters are  packetized and  transmitted
          periodically  as they are in Transparent  Mode, but local editing
          and display features  of Converse Mode are enabled,  and software
          flow  control may  be used.    For a  discussion of  how periodic
          packetizing works,  see the  command PACTIME, which  controls the
          rate and mode of packet assembly.

          You  should  set  CR  OFF  in  this  mode,  since  otherwise  the
          send-packet  character  will  be   inserted  in  the  data  being
          packetized even  though it was  not typed.   In order to  include
          <CR> characters in transmitted packets, set SENDPAC to a normally
          unused  character (e.g., <CTRL-P>),  at which point  the TNC will
          treat <CR> as an ordinary character.

          You can set CPACTIME ON  for a mode of operation similar  to full
          break-in CW, in  which your  text is transmitted  soon after  you
          type it, but  in short bursts of a few  characters, and the other
          station may break in at  will.  Some operators find it  easier to
          carry on a  conversation in  this mode, since  it eliminates  the
          delays while long packets are being typed.



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          CR ON|OFF                                             Default: ON
                                                           Display Group: L

          Parameters:

               ON   The send-packet  character, normally <CR>,  is appended
                    to all packets sent in Converse Mode.

               OFF  The send-packet character is not appended to packets.

          When CR is ON, all packets sent in Converse Mode will include, as
          the last character of the packet, the send-packet character which
          forces the  packet to be  sent.   If CR is  OFF, the  send-packet
          character is interpreted solely as  a command to the TNC, not  as
          data to  be included in the packet,  and furthermore, it will not
          be echoed to the terminal.

          Setting CR ON and SENDPAC $0D  results in a natural  conversation
          mode.  Each  line is sent when a <CR> is  entered, and arrives at
          its destination  with a  <CR> at  the end  of the  line.  If  the
          station at the  other end  reports overprinting of  lines on  his
          display, you  can set LFADD  ON, or  the other   station can  set
          AUTOLF ON.




























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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          CSTATUS
                                                        Display Group: NONE

          CSTATUS is an immediate command which shows the stream identifier
          and  link state of all ten streams (links), the current input and
          output streams,  and whether  or not  each stream  is "permanent"
          (see CONPERM).

          An  example of a display resulting from issuing a CSTATUS command
          is:

            cmd:CS
            A stream - IO Link state is: CONNECTED to 305MLB
            B stream -    Link state is: CONNECTED to AD7I P
            C stream -    Link state is: DISCONNECTED
            D stream -    Link state is: CONNECTED to N0ADI via K9NG-2
           
            ...

            I stream -    Link state is: CONNECT in progress
            J stream -    Link state is: CONNECTED to KV7B via NK6K-1

          The  example above shows the A stream  is assigned both the input
          and output  streams.  The B  stream is connected to  AD7I "perma-
          nently."    All other  streams' states  are  shown as  they might
          normally appear with multiple connections.

























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          CTEXT text                                            Default: ""
                                                          Display Group:  I
          Parameters:

               text Any  combination  of characters  and  spaces,  up to  a
                    maximum length of 120 characters.

          CTEXT  specifies  the text  of  the  packet to  be  sent  after a
          connection is  made, if CMSG is ON.  The default text is an empty
          string, i.e., no message.

          You can send multiple-line  messages by including carriage return
          (<CR>)  characters  in  the text.    The  <CR>  character can  be
          included  by using  the pass  character immediately  preceding it
          (see the PASS  command).  If you enter a  text string longer than
          120 characters, an error message will appear and the command will
          be ignored.

          For example, you might set your CTEXT message to

               I'm not here right now, but you may leave a message.

          To clear the CTEXT text without issuing a RESET command,  use a %
          or & as the first character in the message.

          The CTEXT text is saved in battery-backed RAM.

























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          DAYTIME date&time                                   Default: None
                                                        Display Group: NONE

          Parameters:

               date&time Current date and time to set.

          This command allows you to set the current date and  time for the
          TNC.  The format for entering the date&time is

               yymmddhhmm

          where yy is the last two digits of the  year, mm is the two-digit
          month code (01-12), dd is  date (01-31), hh is the hour  (00-23),
          and mm  is the minute  after the hour  (00-59).  All  these codes
          must  be exactly two digits, so that numbers  from 0 to 9 must be
          entered with leading zeroes.   The TNC does not  check thoroughly
          for the correct number of days in a month, so you should use some
          judgment when you set the date.

          The  date&time parameter  is  used by  the commands  CONSTAMP and
          MSTAMP  to "time stamp" received and monitored messages.  Entries
          in the "heard"  (displayed by  MHEARD) are also  time stamped  if
          date&time has been set.   The TNC's time is  updated continuously
          as  long as it is  powered up.  You must  reset the date and time
          each time  you  turn on  the TNC.    If you  don't  do this,  the
          commands CONSTAMP and MSTAMP will not enable time stamping.

          If you type DAYTIME without a parameter, the TNC will display the
          current date and  time.  The  format of  the display is  dd-mm-yy
          hh:mm if DAYUSA is OFF, and mm/dd/yy hh:mm  if DAYUSA is ON.  The
          format for entering date&time is not affected.  For example,

               cmd:DAYTIME 8402291530

          sets the  date and time  to February 29, 1984  at 3:30 P.M.   The
          display of the date and time, with DAYUSA ON would be:

               cmd:DAYTIME
               02/29/84 15:30:26











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          DAYUSA ON|OFF                                         Default: ON
                                                           Display Group: M

          Parameters:

               ON   Date is displayed in the format mm/dd/yy.

               OFF  Date is displayed in the format dd-mm-yy.

          This command determines the  format for the TNC's display  of the
          date.   If  DAYUSA is ON,  the standard  U.S. format  is used; if
          DAYUSA  is OFF,  the  standard European  format  is used.    This
          command  affects the  format of  the date  display used  in "time
          stamps"  as well as the  display when DAYTIME  is entered without
          parameters.   The format for  entering the time  using DAYTIME is
          not affected.

          For example,  if DAYUSA is  ON, then July  2, 1984 at  9:28:44 AM
          would be displayed as

               cmd:DAYTIME
               07/02/84 9:28:44

          If DAYUSA is OFF the same date and time would appear as

               cmd:DAYTIME
               02-07-84 9:28:44


          DEADTIME n                                            Default: 33
                                                           Display Group: T

          Parameters:

               n         0-250 in 10 mSec increments.

          DEADTIME  specifies the  time it  takes a  station's receiver  to
          detect the  fact that  a remote  transmitter  has keyed  up.   It
          should be set to the time  of the slowest acceptable radio on the
          channel.   It must also allow for any squelch delays and DCD lock
          time.   DWAIT and TXDELAY should  also be set to  this same value
          for everyone in the LAN.

          A fairly fast VHF FM radio-plus-TNC might take 210 mSec (DEA 21),
          while an HF radio-plus-TNC  will usually respond in 80  mSec (DEA
          8).   Some multi-mode radio-plus-TNCs  operating at 1200  bps may
          respond in only 40 mSec (DEA 4).  The default value (DEA 33) will
          safely cover the majority of FM radios in common packet use.



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          DELETE ON|OFF                                        Default: OFF
                                                           Display Group: C

          Parameters:

               ON   The  delete   character  input  editing   character  is
                    <DELETE> ($7F).

               OFF  The  delete   character  input  editing   character  is
                    <BACKSPACE> ($08).

          This  command is  used to  change the  input editing  command for
          character deletion.    When this  character  is typed,  the  last
          character from the input line is deleted.   How the TNC indicates
          the deletion is controlled by the BKONDEL command.

          You can not use this character to delete past the  beginning of a
          line, although  you can  delete <CR>  characters  that have  been
          entered in the text with the pass character.

          To  see a corrected  display of the  current line after  you have
          deleted characters,  type the redisplay-line character,  which is
          set by the REDISPLA command.

          This command does not work while in transparent mode.


























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          DIGIPEAT ON|OFF                                       Default: ON
                                                           Display Group: L

          Parameters:

               ON   The TNC will digipeat packets if requested.

               OFF  The TNC will not digipeat packets.

          When  this parameter  is ON,  any packet  received that  has your
          TNC's  callsign  (including SSID)  in  the digipeat  list  of its
          address field  will be retransmitted.   Each station  included in
          the  digipeat list  relays the  packet in  its turn,  marking the
          packet so that it will not accidentally relay it twice (unless so
          requested), and so that the stations will relay the packet in the
          correct order.   Digipeating takes place  concurrently with other
          TNC  operations and does not interfere with normal operation of a
          packet station.

          In the spirit  of cooperation typical  of Amateur operation,  you
          will probably want to set DIGIPEAT ON most of the time.  However,
          you might want to disable  digipeating if you're not home,  or if
          your transmit relay makes enough noise to wake you up at night.

          The command  HID enables automatic transmission of identification
          packets if your station is acting as a digipeater.

























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          DISCONNE
                                                        Display Group: NONE

          DISCONNE  is an immediate command.  It will initiate a disconnect
          request  with  the currently  connected  station.   A  successful
          disconnect results in the display of:

               *** DISCONNECTED

          Other  commands may  be entered  while the  disconnect is  taking
          place, although  connects are disallowed until  the disconnect is
          completed.  If the  retry count is exceeded while waiting for the
          other station to  acknowledge, the TNC moves to  the disconnected
          state.   If  a disconnect  command is  entered while  the TNC  is
          disconnecting, the retry count is  immediately set to the maximum
          number.  In either case, the disconnect message is 

               *** retry count exceeded
               *** DISCONNECTED

          Disconnect  messages  are  not  displayed  when  the  TNC  is  in
          Transparent Mode.


          DISPLAY [class]
                                                        Display Group: NONE

          Parameters:

               class     Optional  parameter-class  identifier, one  of the
                         following:

          ASYNC          display asynchronous port parameters
          CHARACTE       display special characters
          HEALTH         display health counters/LEDs
          ID             display ID parameters
          LINK           display link parameters
          MONITOR        display monitor parameters
          TIMING         display timing parameters

          DISPLAY is an immediate command, and with no class parameter will
          cause  all control  parameters  and their  current  values to  be
          displayed.  Sub-groups of related parameters can  be displayed by
          specifying the  optional parameter-class  (e.g.,  DISPLAY A  will
          list  all  the   asynchronous  port   parameters).     Individual
          parameters can be  displayed by entering the  parameter name with
          no  options (e.g., entering AWLEN will cause the present value of
          AWLEN to be displayed).



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          DWAIT n                                               Default: 33
                                                           Display Group: T

          Parameters:

               n         0 -  250, specifying  default wait  time in  10 ms
                         intervals.

          This value is used  to avoid collisions with digipeated  packets.
          The TNC will  wait the default wait time  after last hearing data
          on  the channel before it  begins its own  keyup sequence, unless
          the  TNC is waiting to  transmit digipeated packets.   This value
          should  be  agreed  on  by  all members  of  a  local  area  when
          digipeaters are  used  in the  area.    The best  value  will  be
          determined  by experimentation,  but will  be a  function of  the
          keyup time (TXDELAY) of the digipeater stations.

          This feature  is intended to help alleviate the drastic reduction
          of throughput  that occurs on  a channel when  digipeated packets
          suffer collisions.   It  is necessary because  digipeated packets
          are not retried  by the digipeater, but must  be restarted by the
          originating  station.   If all  stations  specify a  default wait
          time, and the  right value  of n is  chosen, the digipeater  will
          capture  the  frequency every  time it  has  data to  send, since
          digipeated packets are sent without this delay.

          NOTE:  DWAIT is used for other purposes in many LANs.  Do not set
          DWAIT to 0 just because you think there are no digipeaters in use
          on the channel you are occupying!






















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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          ECHO ON|OFF                                           Default: ON
                                                           Display Group: A

          Parameters:

               ON   Characters received  from the computer or  terminal are
                    echoed by the TNC.

               OFF  Characters are not echoed.

          This command  controls local  echoing by  the TNC when  it is  in
          Command  or  Converse  Mode.    Local  echoing  is   disabled  in
          Transparent Mode.

          If you don't  see your input on the display,  you should set ECHO
          ON.   If  you see  two copies  of every  character you  type, you
          should  set  ECHO  OFF.    If you  see  the  characters  you type
          displayed correctly, you have ECHO set correctly.


          ESCAPE ON|OFF                                        Default: OFF
                                                           Display Group: A

          Parameters:

               ON   The <ESCAPE> character ($1B) is output as "$" ($24).

               OFF  The <ESCAPE> character is output as <ESCAPE> ($1B).

          This command specifies the character which will be output when an
          <ESCAPE>  character is to be sent  to the terminal.  The <ESCAPE>
          translation is disabled in Transparent Mode.

          This  command is  provided because  some terminals,  and computer
          programs  that emulate  such  terminals, interpret  the  <ESCAPE>
          character  as a special command prefix.  Such terminals may alter
          their  displays  depending   on  the  characters   following  the
          <ESCAPE>.   If you have such a terminal, you can protect yourself
          from  unexpected  text sequences  and  from  other packeteers  by
          setting ESCAPE ON.

          See  also the  MFILTER  command, which  allows general  character
          stripping  (rather  than  character  translation)   in  monitored
          packets.







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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          FIRMRNR ON|OFF                                        Default: ON
                                                           Display Group: L

          Parameters:

               ON   When this TNC's buffers fill, an RNR is sent.  When the
                    buffers are  no  longer full,  an RR  command frame  is
                    sent.

          When this TNC receives an  RNR, it will not poll the  sending TNC
          until [T0*10 seconds].   T0 =  CHECKtime*8 unless CHECKtime*8  is
          <30 or >253 in which case T0 = 12.

               OFF  When  this  TNC's buffers  fill, an  RNR  is sent  as a
                    response to an I frame.

          When  this TNC  receives an  RNR, it  will resend the  data every
          FRACKtime (T1) until an RR is received.

          When OFF, standard AX.25 Level 2  Version 2.0 protocol procedures
          are used.   If a  TNC sending data  receives an RNR,  meaning the
          remote  TNC  cannot  accept  more  data,  the  sending  TNC  will
          continuously re-send the data  every T1 (FRACK) time until  an RR
          is  received, meaning  the remote  TNC accepted  the data.   This
          often results in a lot of unnecessary channel congestion.

          When  FIRMRNR is ON, this TNC will stop sending data upon receipt
          of an  RNR.  If  the remote TNC does  not send an  RR before [T0]
          (see  above), this TNC will poll the remote  TNC to be sure it is
          still active.  If this TNC sent the RNR, then it  will send an RR
          when its buffers have cleared to allow more data to be received.

          NOTE:  The  remote TNC  should be capable  of FIRMRNR  operation.
          This mode is operable  with all TNCs having a FIRMRNR settable to
          ON, and  with most  network  nodes.   If the  remote  TNC is  not
          capable of FIRMRNR operation,  and if the channel is  poor, there
          will  be additional  delays in  getting data  passed between  the
          TNCs.













                                          95








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          FLOW ON|OFF                                           Default: ON
                                                           Display Group: A

          Parameters:

               ON   Type-in flow control is active.

               OFF  Type-in flow control is disabled.

          When type-in flow control is  enabled, any character entered from
          the  terminal will  halt output  to the  terminal  until:   (1) a
          packet is forced (in  Converse Mode); (2) a line is completed (in
          Command  Mode); (3)  the packet  length is  exceeded; or  (3) the
          terminal  output buffer fills up.   Canceling the current command
          or packet or typing the  redisplay-line character will also cause
          output   to  resume.    Type-in  flow  control  is  not  used  in
          Transparent Mode.

          Setting FLOW  ON will  keep received  data from  interfering with
          data entry.  If you  (and the person you are talking to) wait for
          a packet from  the other end before starting  to respond, you can
          set FLOW  OFF.  Some Bulletin  Board programs may  work best with
          FLOW OFF.  Some  computers with "software UARTs" may be unable to
          send and receive  data at the same time; users  of such computers
          should set FLOW ON.


          FRACK n                                                Default: 8
                                                           Display Group: T

          Parameters:

               n         0 -  15, specifying frame  acknowledgment time-out
                         (T1) in 1 second intervals.

          After  transmitting a  packet requiring  acknowledgment, the  TNC
          will  wait   for  the   frame   acknowledgment  time-out   before
          incrementing the retry counter  and sending the frame again.   If
          the packet address includes digipeater requests, the time between
          retries will be adjusted to

                    Retry interval = n * (2*m + 1)

          where m is the number of digipeaters.

          When a retried packet is sent, a random wait time is added to any
          other wait times in use.  This  is to avoid lockups in which  two
          TNCs repeatedly send packets which collide with each other.



                                          96








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          FULLDUP ON|OFF                                       Default: OFF
                                                           Display Group: L

          Parameters:

               ON   Full duplex mode is enabled.

               OFF  Full duplex mode is disabled.

          When full  duplex mode is disabled, the TNC makes use of the Data
          Carrier Detect signal  from the  modem to  avoid collisions,  and
          acknowledges  multiple packets  in a  single transmission  with a
          single acknowledgment.  When full duplex mode is enabled, the TNC
          ignores  the DCD  signal  and acknowledges  packets individually.
          The latter mode  is useful for full-duplex  radio operation, such
          as through the Microsats.  It should not be used unless both your
          station  and   the  station   you  are  communicating   with  are
          full-duplex stations.

          You may find full-duplex mode useful for some testing operations,
          such as analog- or digital-loopback tests.

          Note that certain  timers, such  as DWAIT, are  disabled when  in
          FULLDUP mode.



























                                          97








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          HEADERLN ON|OFF                                      Default: OFF
                                                           Display Group: M

          Parameters:

               ON   The  header for  a  monitored packet  is  printed on  a
                    separate line from the packet text.

               OFF  The  header and  packet text  of monitored  packets are
                    printed on the same line.

          This command  affects the  display format for  monitored packets.
          If HEADERLN is OFF, the address information is displayed with the
          packet:

               KV7D>N2WX: Go ahead and transfer the file.

          If HEADERLN is ON, the address information is displayed, followed
          by the packet text on a separate line:

               N2WX>KV7D:
               Sorry, I'm not quite ready yet.

          If you have  set MRPT ON or enabled  MSTAMP, you may wish  to set
          HEADERLN  ON, as the packet header quickly becomes long enough to
          fill a line when these functions are active.

























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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          HEALLED  ON|OFF                                      Default: OFF
                                                           Display Group: H

          Parameters:

               ON   The TNC will "dither" the CON and STA LEDs.

               OFF  The TNC will  control the  CON and STA  LEDs in  normal
                    fashion.


          This command allows the user to redefine the functions of the two
          CPU controllable LEDs (i.e. the STAtus and CONnect LEDs).

          When HEALLED  is set ON, the  two LEDs flash in  a seeming random
          fashion.   At a glance, the  user may make a  judgment on whether
          the  software has crashed, since the LEDs will probably not flash
          if the software fails catastrophically.

          With HEALLED  set OFF, the  LEDs function normally.   The CON LED
          glows  when   the  current  stream   is  in   the  connected   or
          disconnecting state,  and  the STA  LED  glows when  the  current
          stream has unacknowledged packets in the transmit buffer.


          HID ON|OFF                                           Default: OFF
                                                           Display Group: I

          Parameters:

               ON   Enables HDLC identification by a digipeater.

               OFF  Disables HDLC identification.

          This  command is  used  to  enable  or  disable  the  sending  of
          identification packets by  the TNC.  If HID is  OFF, the TNC will
          never send  an identification packet.  If HID is ON, the TNC will
          send an identification packet every 9.5 minutes if the station is
          digipeating  packets.  The ID command allows the operator to send
          a final identification packet  if the station is being  taken off
          the air.

          An  identification consists  of an  unsequenced information  (UI)
          frame  whose  data field  is  your station  identification.   The
          identification packet is addressed to the "CQ" address set by the
          UNPROTO command.  Your station identification is your callsign as
          set by MYCALL, with "/R" appended.




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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          ID
                                                        Display Group: NONE

          ID is  an immediate  command.   It  will send  a special  identi-
          fication  packet.  ID can be used to force a final identification
          packet to be sent as a  digipeater station is being taken off the
          air.   The  identification  packet  will  be  sent  only  if  the
          digipeater   has   transmitted    since   the   last    automatic
          identification.

          An identification consists  of an  UI frame whose  data field  is
          your  station  identification.    The  identification  packet  is
          addressed to the  "CQ" address set by the UNPROTO  command.  Your
          station identification is  your callsign as  set by MYCALL,  with
          "/R" appended.




































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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          KISS ON|OFF                                          Default: OFF
                                                           Display Group: L

          Parameters:

               ON   Serial Line  Interface Protocol (SLIP) is  used between
                    the  TNC and the attached computer.  The TNC executes a
                    very  limited  instruction  set,   arbitrating  channel
                    access only and depending on the computer to handle all
                    Level Two and higher protocol issues.

               OFF  The  TNC  operates  using  the  commands  and  messages
                    documented  herein.    This   is  the  normal  mode  of
                    operation.

          This  command is used to enter the "KISS" mode for operation with
          various experimental  protocols.   KISS is used  with intelligent
          host computers.   The most  popular use has  been in  conjunction
          with the KA9Q TCP/IP networking software, available from TAPR and
          elsewhere.

          To operate KISS  with this  release, enter the  command KISS  ON,
          then the command RESTART (NOT RESET!).  The CON and STA LEDs will
          flash three  times when initially  activated.  This  command will
          then have effect for  subsequent power on/off cycles.   To return
          to normal operation, enter the command PARAM <device> 255 at the 

                NET> 

          prompt if you are  running the KA9Q TCP/IP software package.   If
          you are  not using this  package, send the three  bytes $C0, $FF,
          $C0  to the TNC to restore normal  operation.  If you cannot send
          these character values with  the software you intend to  use, you
          must power the  TNC off,  then disconnect the  bbRAM battery  for
          several minutes, then reconnect the battery and power up again to
          restore normal operation.















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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          The commands available in Kiss Mode are:

          Command   Function  Comments

          0         Data Frame     The  rest of  the  frame is  data to  be
                                   sent.

          1         TXDELAY   The  next byte  is is  the transmitter  keyup
                              time in 10 mSec  units, with a default of  50
                              (500 mSec).

          2         P         The next  byte is the  persistence parameter,
                              p,   scaled  to   the  range   0-255.     The
                              probability  of  transmitting  at   the  next
                              opportunity is p/255.  The default is 64 (for
                              a probability of 0.25).

          3         SlotTime  The next byte is the slot interval in 10 mSec
                              increments.  The default is 10 (100 mSec).

          4         TXtail         The next  byte is  the time to  hold the
                                   transmitter after the FCS has been sent,
                                   in  10  mSec  units.    The  command  is
                                   obsolete    and    is    included    for
                                   completeness     with    earlier     im-
                                   plementations.

          5         FullDuplex     The  next  byte  is  0  for  half-duplex
                                   (normal)  or any  other number  for full
                                   duplex   (e.g.,   for   operation   with
                                   MicroSats).

          FF        Return    Exit KISS and resume normal TNC operation.

          NOTE:    The  TNC  will  only  return  type  0  frames  (received
          information).  Thus, the  computer cannot interrogate the TNC  to
          find the values of the other command types.


          KISSM     {immediate command}

          This command  may be used  to cause the TNC  to immediately begin
          running the KISS code.








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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          LCALLS call1[,call2...,call8]                         Default: ""
                                                           Display Group: M

          Parameters:

               call Callsign list.  Up to 8 calls, separated by commas.

          Each callsign may include an optional sub-station ID specified as
          -n  immediately following  the  call.    This  command  works  in
          conjunction with BUDLIST and allows selective monitoring of other
          packet stations.  These two commands determine which packets will
          be displayed when  you have  set MONITOR ON.   BUDLIST  specifies
          whether the callsigns in the list are the ones you want to ignore
          or, alternatively, are the only ones you want to listen to.

          If you want to listen  only for packets from a limited  list, you
          should enter your selected list with LCALLS and set BUDLIST ON.

          If you want  to ignore packets  from a  limited list, you  should
          list the callsigns to ignore in LCALLS and set BUDLIST OFF.

          The list of calls in the LCALLS buffer is saved in battery-backed
          RAM.  The calls may be cleared without issuing a RESET command by
          entering a "%" or a "&" character as a callsign.



























                                         103








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          LCOK ON|OFF                                           Default: ON
                                                           Display Group: A

          Parameters:

               ON   The TNC will send lower case characters to the computer
                    or terminal.

               OFF  The TNC  will translate lower case  characters to upper
                    case.

          If LCOK is OFF, lower case characters will be translated to upper
          case  before being output to the terminal.  This case translation
          is disabled in Transparent Mode.  Input characters and echoes are
          not case translated.

          If  your  computer  or  terminal  does  not  accept  lower   case
          characters it may react badly if the TNC sends such characters to
          it.   This  command  allows  you  to  translate  all  lower  case
          characters received in packets, as well as messages from the TNC,
          to upper case.

          Since echoes of  the characters  you type are  not translated  to
          upper case, you can use this  command to make your display easier
          to read  when you are conversing  in connected mode.   If you and
          the other station's operator set LCOK OFF, you can each type your
          own  messages in lower case and see incoming packets displayed in
          upper  case.   This  makes it  easy  to distinguish  incoming and
          outgoing lines.






















                                         104








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          LCSTREAM  ON|OFF                                      Default: ON
                                                           Display Group: C

          Parameters:

               ON   The  TNC  will   translate  the  character  immediately
                    following  the  STREAMSWITCH  character  to  upper case
                    before processing it.

               OFF  The   TNC  will   process  the   character  immediately
                    following the STREAMSWITCH character as it is entered.


          When  operating  multi-connect,  the  user must  enter  a  stream
          identifier (default A through J) after the STREAMSWITCH character
          (default  |) to  select  a  new  logical  stream  to  send  data.
          Normally,  the stream  identifier must  be in  upper case,  or an
          error message will result.

          When  LCSTREAM is  ON,  the character  immediately following  the
          streamswitch character  is converted  to upper case  before being
          acted  upon.     Thus,   the  case  (upper   or  lower)   becomes
          insignificant.  Use of  LCSTREAM is useful if  you are typing  in
          lower  case and  don't want  to be  bothered with  remembering to
          switch to upper case when changing streams.


          LFADD ON|OFF                                         Default: OFF
                                                           Display Group: L

          Parameters:

               ON   A <LF> character is added to outgoing packets following
                    each <CR> transmitted in the packet.

               OFF  No <LF> is added to outgoing packets.

          This  function  is  similar  to  AUTOLF,  except  that  the  <LF>
          characters  are added  to  outgoing packets  rather than  to text
          displayed locally.  This feature is included in order to maintain
          compatibility with other packet radio controllers.  If the person
          you  are talking  to reports  overprinting of  packets from  your
          station you should  set LFADD  ON.  This  character insertion  is
          disabled in Transparent Mode.







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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          LFIGNORE ON|OFF                                      Default: OFF
                                                           Display Group: L

          Parameters:

               ON   TNC will ignore <LF> characters.

               OFF  TNC will respond to <LF> characters.

          This command controls whether  TNC 2 responds to ASCII  Line Feed
          (<LF> $0A) characters  or ignores  them in  command and  converse
          modes.

          When turned on, line  feeds are totally ignored except  in trans-
          parent mode.


          MALL ON|OFF                                           Default: ON
                                                           Display Group: M

          Parameters:

               ON   Monitored  packets include both "connected" packets and
                    "unconnected" packets.

               OFF  Monitored packets include only "unconnected" packets.

          This command determines the class of packets which are monitored.
          If MALL is OFF, only otherwise eligible packets (as determined by
          the  BUDLIST and  LCALLS  commands) sent  by  other TNCs  in  the
          unconnected mode are  displayed.   This is the  normal manner  of
          operation when this TNC is being used to talk to a group of  TNCs
          all of which are unconnected.

          If  MALL  is ON,  all  otherwise eligible  frames  are displayed,
          including those sent between two other connected TNCs.  This mode
          may be enabled for diagnostic purposes or for "reading the mail."














                                         106








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          MAXFRAME n                                             Default: 4
                                                           Display Group: L

          Parameters:

               n         1 - 7, signifying a number of packets.

          MAXFRAME sets  an upper  limit  on the  number of  unacknowledged
          packets which the TNC can have outstanding at any one time.  This
          is also the  maximum number  of contiguous packets  which can  be
          sent  during any given transmission.  If  some but not all of the
          outstanding  packets are  acknowledged, a  smaller number  may be
          transmitted the next  time, or new frames may be  included in the
          retransmission, so that the  total unacknowledged does not exceed
          n.

          If  you  perform  file  transfers,  you  should  experiment  with
          MAXFRAME and  PACLEN.  If the  link is good, there  is an optimum
          relationship between the parameters set by these commands so that
          the maximum number of characters outstanding  does not exceed the
          packet receive buffer space of the TNC receiving the data.






























                                         107








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          MCOM ON|OFF                                          Default: OFF
                                                           Display Group: M

          Parameters:

               ON   Connect,  disconnect, UA,  DM,  I and  UI   frames  are
                    monitored.

               OFF  Only information frames (I and UI) are monitored.

          This command enables monitoring  of connect and disconnect frames
          when MONITOR  is ON.   When MCOM is  OFF, only I  frames (packets
          containing user information) will be displayed.

          When MCOM is on, all control fields are decoded (invalid ones are
          marked  with  ????).    For  I  and  S  frames,  sequence  number
          information is also presented.  Frames compatible with the  AX.25
          Level  2.0 standard  are  also decoded  as to  the  state of  the
          Command/Response (C/R) and Poll/Final (P/F) bits.

               Ex:  WA7GXD>KV7B <I C S0 R0>:
                    Hi Dan,

                    WA7GXD>KV7B <I C P S1 R0>:
                    have you been on EIES lately?

                    KV7B>WA7GXD <RR R F R2>
                    KV7B>WA7GXD <I C P S1 R2>:
                    I was just thinking about that.  I heard that
                    @(username) made some real unbelievable comment on it!

                    WA7GXD>KV7B <RR R F R2>
                    WB2SPE>KV7B <C>
                    KV7B>WB2SPE <DM>
                    KV7B>WA7GXD <I C P S2 R2):
                    Good conditions now...

                    WA7GXD>KV7B <RR R F R3>
                    WA7GXD>KV7B <I C P S2 R3>:
                    Yes @(username) did.  It was quite remarkable.

          As  with  other  monitor  commands, the  stations  monitored  are
          determined by BUDLIST and LCALLS.








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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          MCON ON|OFF                                           Default: ON
                                                           Display Group: M

          Parameters:

               ON   Monitor mode remains active when the TNC is connected.

               OFF  Monitor mode is disabled while the TNC is connected.

          If MCON is ON,  the MONITOR command will enable  monitoring while
          your TNC  is connected  to  another TNC.   If  MCON  is OFF,  the
          display of monitored packets is suspended when a  connect occurs,
          and is resumed when the TNC is disconnected.

          If  you  want to  see  all packets  displayed  when  you are  not
          connected  but have such  display suppressed when  you connect to
          another station, you should set MCON OFF.


          MFILTER n1[,n2[,n3[,n4]]]                           Default: None
                                                           Display Group: M

          Parameters:

               n         0 - $7F, specifying an  ASCII character code.   Up
                         to 4 characters may be specified.

          This command allows  you to specify characters  to be "filtered,"
          or eliminated from  monitored packets.   The  parameters n1,  n2,
          etc., are the ASCII codes for the  characters you want to filter.
          You can enter the code in either hex or decimal.

          For example, if  a <CTRL-L>  character causes your  screen to  be
          cleared,  and you don't want this to  happen, you can set MFILTER
          12.  If  you also  want to eliminate  <CTRL-Z> characters,  which
          some  computers interpret  as  end-of-file markers,  you can  set
          MFILTER 12,26.


          MHCLEAR
                                                        Display Group: NONE

          MHCLEAR is an immediate command.  It causes the list of  stations
          heard  to be  cleared.  You  can use this  command in conjunction
          with MHEARD to keep track of the stations on the air over a given
          period of time, such as  an evening or a week.  Clear the list of
          stations  heard  when  you  first  begin to  monitor  the  packet
          activity.



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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          MHEARD
                                                        Display Group: NONE

          MHEARD is an immediate command.  It causes the TNC to display the
          list of  stations that have  been heard since  the last time  the
          command  MHCLEAR was  given.   Stations  that  are heard  through
          digipeaters are  marked with a * in the  heard log.  If you clear
          the list of stations heard at the beginning of a session, you can
          use this  command to easily  keep track of the  stations that are
          active  during that period.  The maximum number of heard stations
          that can  be logged is 18.   If more stations  are heard, earlier
          entries are  discarded.  Logging  of stations  heard is  disabled
          when PASSALL is ON.

          If the  DAYTIME command has been  used to set the  date and time,
          entries in the heard log will be time stamped.  For example,

               cmd:MHEARD
               K4NTA*    06/09/85  21:08:19
               WA4ITD*   06/09/85  21:08:17
               W1BEL-2*  06/09/85  21:06:18
               K4NTA-2*  06/09/85  20:57:35
               N2WX
               cmd:

          Note  that no  daytime string is  displayed next  to N2WX.   This
          indicates  that when N2WX was  last heard the  clock had not been
          set.


          MNONAX25 ON|OFF                                      Default: OFF
                                                           Display Group: M

          Parameters:

               ON   Monitors all frames with valid CRC.

               OFF  Monitors  AX.25  Level   2  Protocol  frames  with   no
                    higher-level protocols (PID = F0).

          When OFF, only AX.25  Level 2 protocol frames will  be displayed.
          Any packets with level 3 or level 4 protocols  will be inhibited.
          Thus, NET/ROM, TCP/IP, ROSE, etc., networking frames  will not be
          displayed.   These frames often have binary values buried in them
          which cause undesirable responses on a normal screen display.

          When  ON, any packet or frame with  a valid CRC will be displayed
          regardless of protocol.



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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          MONITOR ON|OFF                                        Default: ON
                                                           Display Group: M

          Parameters:

               ON   Monitoring of packet activity is enabled.

               OFF  Monitoring of packet activity is disabled.

          If MONITOR  is ON and the TNC is not in Transparent Mode, packets
          not addressed to your TNC may be displayed.  The addresses in the
          packet are displayed along  with the data portion of  the packet,
          e.g.:

               N2WX>W5FD-3: I'm ready to transfer the file now.

          The calls  are separated  by a ">"  and the sub-station  ID field
          (SSID) is  displayed if it is  other than 0.   The MALL, BUDLIST,
          and LCALLS commands determine which  packets are to be monitored.
          The MCON command controls the action of monitor mode when the TNC
          is connected.  All monitor functions are disabled  in Transparent
          Mode.

          The format of the monitor display  is controlled by HEADERLN.  If
          you want to see the station addresses on a separate line from the
          text, you can  set HEADERLN ON.   MRPT enables monitoring  of the
          digipeater route  as well as source and destination addresses for
          each packet.   MSTAMP includes a time stamp with the addresses if
          DAYTIME has been set.






















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          MRPT ON|OFF                                           Default: ON
                                                           Display Group: M

          Parameters:

               ON   Display the stations in the digipeat path for monitored
                    packets.

               OFF  Display  only the  source and destination  stations for
                    monitored packets.

          This command affects the way monitored packets are displayed.  If
          MRPT is OFF, only the originating station and the destination are
          displayed  for  monitored packets.   If  MRPT  is ON,  the entire
          digipeat list  is displayed  for monitored packets,  and stations
          that  have  already  relayed  the packet  are  indicated  with an
          asterisk.

          For example,

               WB9FLW>AD7I,K9NG*,N2WX-7:Hi Paul.

          This  packet, sent from WB9FLW to AD7I,  has been relayed by K9NG
          but  not by  N2WX-7.   With MRPT  OFF, the  same packet  would be
          displayed as

               WB9FLW>AD7I:Hi Paul.

          Setting  MRPT ON increases the length of the address display, and
          you may wish to set HEADERLN  ON as well to display this informa-
          tion on a separate line.




















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          MSTAMP ON|OFF                                        Default: OFF
                                                           Display Group: M

          Parameters:

               ON   Monitored frames are time stamped.

               OFF  Monitored frames are not time stamped.

          This command  enables time  stamping of  monitored packets.   The
          date and time information is then available for use for automatic
          logging  of packet activity or other  computer applications.  The
          date and time  are set initially by the DAYTIME  command, and the
          date format is determined by the DAYUSA command.

          Setting  MSTAMP ON increases  the length of  the address display,
          and  you may  wish to  set HEADERLN  ON as  well to  display this
          information on a separate line.

































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          MYALIAScall[-n]                                  Default: <blank>
                                                           Display Group: I

          Parameters:

               call Alternative identity of your TNC.

               n         0  - 15,  an optionally  specified sub-station  ID
          (SSID).

          This command  specifies an  alternative callsign (in  addition to
          the callsign specified in MYCALL) for use as a digipeater only.

          In some  areas, wide coverage digipeaters  operators have changed
          the callsign of their  machine to a shorter and  (usually) easier
          to remember identifier.   International Civil  Aviation Organiza-
          tion (ICAO) airport  identifiers, sometimes  combined with  tele-
          phone area codes, have been used.

          Use of this  command permits  HID to identify  normally with  the
          MYCALL-specified  callsign  yet  permit  an  alternative  (alias)
          repeat-only "callsign."


          MYCALL call[-n]                                 Default: NOCALL-0
                                                           Display Group: I

          Parameters:

               call Callsign of your TNC.

               n         0  - 15,  an optionally  specified  sub-station ID
          (SSID).

          This command tells  the TNC what its callsign is.   This callsign
          will  be placed  in  the  FROM  address  field  for  all  packets
          originated by your TNC.  It will accept frames with this callsign
          in  the TO  field  and relay  frames  with this  callsign  in the
          digipeat field (if DIGIPEAT is ON).  MYCALL will also be used for
          identification packets (see HID and ID).

          The  default callsign must be changed for proper operation of the
          protocols.  There should never be more than one station with  the
          same callsign (including SSID) on the air at once.   The SSID can
          be used to distinguish  two stations with the same  Amateur call.
          The SSID will be 0 unless explicitly set to another value.





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          NEWMODE ON|OFF                                       Default: OFF
                                                           Display Group: L

          Parameters:

               ON   Switching to data  transfer mode occurs at  the time of
                    connection, or the issuing  of the CONNECT command, and
                    return to  command mode  is  automatic at  the time  of
                    disconnection.

               OFF  Switching  to  data transfer  mode  occurs  at time  of
                    connection  and no  return  to command  mode occurs  at
                    disconnection.

          The NEWMODE command may be used to select the way the TNC behaves
          when connections are made and broken.

          If NEWMODE is OFF, the TNC  will remain in Command Mode after you
          issue  a   CONNECT  command   until  a  connection   is  actually
          established.  When  the connection is  established, the TNC  will
          enter Converse Mode or Transparent Mode, depending on the setting
          of CONMODE.  When  the connection is terminated, the  TNC remains
          in  Converse or  Transparent Mode  unless you  have forced  it to
          return to Command Mode.  This is the same as the behavior  of TNC
          1 (running version 3.x software) under these conditions.

          If NEWMODE is ON, the TNC will enter Converse Mode or Transparent
          Mode as soon  as you issue a CONNECT command, without waiting for
          the  connection to  be established.   Anything  you type  will be
          packetized  to be  transmitted once  the connection  is complete.
          When the connection is  broken, or if the connect  attempt fails,
          the TNC will return to Command Mode.

          If you  have a Bulletin Board program designed to work with TNC 1
          you should set NEWMODE OFF if  the program relies on the sequence
          of actions  used  by TNC  1.   Otherwise, you  should choose  the
          setting for NEWMODE that seems most convenient to you.














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          NOMODE ON|OFF                                        Default: OFF
                                                           Display Group: L

          Parameters:

               ON   The TNC  will only  switch modes (command,  converse or
                    transparent) upon explicit command.

               OFF  The  TNC  will  switch  modes in  accordance  with  the
                    setting of NEWMODE.


          When NOMODE is ON, the TNC  will never change between CONVERSE or
          TRANSPARENT  mode to  COMMAND mode  (or vice-versa)  on  its own.
          Only  user commands (CONV, TRANS,  or ^C) may  change the type-in
          mode.

          If  NOMODE  is  OFF, then  automatic  mode  switching  is handled
          according to the setting of the NEWMODE command.


          NUCR ON|OFF                                          Default: OFF
                                                           Display Group: A

          Parameters:

               ON   <NULL> characters  are sent  to the  terminal following
                    <CR> characters.

               OFF  <NULL>  characters  are   not  sent  to   the  terminal
                    following <CR> characters.

          This command causes transmission of <NULL> characters (ASCII code
          $00), producing an effective delay following any <CR> sent to the
          terminal.  The number  of <NULL> characters is determined  by the
          command  NULLS.     This  delay  is  required  by  some  hardcopy
          terminals.  You need to  set NUCR ON if your terminal  misses one
          or more  characters after responding to  a <CR>.  If  this is the
          case, you will sometimes see overtyped lines.












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          NULF ON|OFF                                          Default: OFF
                                                           Display Group: A

          Parameters:

               ON   <NULL> characters  are sent  to the  terminal following
                    <LF> characters.

               OFF  <NULL>  characters  are   not  sent  to   the  terminal
                    following <LF> characters.

          This command causes transmission of <NULL> characters (ASCII code
          $00), producing an effective delay following any <LF> sent to the
          terminal.  The number  of <NULL> characters is determined  by the
          command NULLS.  This delay is required by some display terminals.
          You  need  to  set NULF  ON  if  your  terminal sometimes  misses
          characters at the beginning of the line.


          NULLS n                                                Default: 0
                                                           Display Group: A

          Parameters:

               n         0 - 30, specifying the number of <NULL> characters
                         to send after <CR> or <LF>.

          This  command specifies  the number  of <NULL>  characters (ASCII
          code  $00) to send to the terminal after  a <CR> or <LF> is sent.
          In addition  to setting this  parameter value,  NUCR and/or  NULF
          must be  set to indicate whether nulls are to be sent after <CR>,
          <LF>,  or both.  Devices requiring nulls after <CR> are typically
          hard-copy devices requiring time  for carriage movement.  Devices
          requiring  nulls  after  <LF>  are typically  CRTs  which  scroll
          slowly.   Extra  null characters  are sent  only in  Converse and
          Command Modes.


          OUT nn    0<=nn<=255

          The value  'nn' is sent  to the TNC's z/80  i/o port 0BFH.   Note
          that the last value 'nn' is  sent to the i/o port frequently, but
          not immediately.  In this context, 'frequently'  means many times
          per second, and 'not immediately' means within at most 100ms.







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          PACLEN n                                             Default: 128
                                                           Display Group: L

          Parameters:

               n         0 - 255, specifying the maximum length of the data
                         portion of a packet.  The value 0 is equivalent to
                         256.

          The TNC will automatically  transmit a packet when the  number of
          input bytes  for a packet reaches n.  This  value is used in both
          Converse and Transparent Modes.

          If you perform  file transfers, you  should experiment with  both
          MAXFRAME and  PACLEN.  If the  link is good, there  is an optimum
          relationship between the parameters set by these commands so that
          the maximum number of characters outstanding does not exceed  the
          packet receive buffer space of the TNC receiving the data.

          Note:  Although there  is no requirement for two  TNCs exchanging
          data  to have  the  same PACLEN  value,  allowing more  than  128
          characters  of data  in a  packet may  be incompatible  with some
          varieties of TNCs.


          PACTIME EVERY|AFTER n                           Default: AFTER 10
                                                           Display Group: T

          Parameters:

               n         0 - 250, specifying 100 ms intervals.

               EVERY     Packet time-out occurs every n*100 milliseconds.

               AFTER     Packet  time-out  occurs  when n*100  milliseconds
                         elapse  with   no  input  from  the   computer  or
                         terminal.

          This  parameter is always used in Transparent Mode, and will also
          be  used  in Converse  Mode if  CPACTIME is  ON.   When  EVERY is
          specified, input  bytes are packaged and  queued for transmission
          every n*100 ms.  When AFTER is specified, bytes are packaged when
          input from the  terminal stops for n*100  ms.  In no case  will a
          zero  length packet  be produced,  and the  timer is  not started
          until  the first byte is entered.  A value of 0 for n is allowed,
          and causes packets to be generated with no wait time.





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          PARITY n                                        Default: 3 (even)
                                                           Display Group: A

          Parameters:

               n         0 -  3, selecting a  parity option from  the table
                         below.

          This command sets the  parity mode for terminal or  computer data
          transfer according to the following table:

                               n     Parity

                               0     no parity
                               1     odd parity
                               2     no parity
                               3     even parity

          The parity  bit, if present,  is automatically stripped  on input
          and   not  checked  in  Command  Mode  and  Converse  Mode.    In
          Transparent Mode,  all eight bits,  including parity if  any, are
          transmitted in  packets.  If "no  parity" is set and  AWLEN is 7,
          the eighth bit will be set to 0 in Transparent Mode.




























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          PASS n                                      Default: $16 <CTRL-V>
                                                           Display Group: C

          Parameter:

               n         0 - $7F, specifying an ASCII character code.

          This command  selects the  ASCII  character used  for the  "pass"
          input editing command.  The parameter n is the ASCII code for the
          character  you want  to type  in order  to include  the following
          character in a packet or text string.  You can enter the  code in
          either hex or decimal.

          You can use this character to send any character in packets, even
          though  that  character may  have  some  special function.    For
          example, suppose you have set COMMAND 3, specifying that <CTRL-C>
          is  your Command  Mode entry  character.   If you use  a Bulletin
          Board  program  that  requires a  <CTRL-C>  to  escape  from some
          operation, you will type

               <CTRL-V> <CTRL-C>

          to insert a <CTRL-C> character in your packet.  Of course, if you
          do this frequently you would be better off to change your Command
          Mode entry character.

          A  common use  for the  pass  character is  to allow  <CR> to  be
          included in the  BTEXT and  CTEXT messages.   Similarly, you  can
          include  <CR> in  text when  you are  in Converse  Mode, to  send
          multi-line packets.  (The default send-packet character is <CR>.)





















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          PASSALL ON|OFF                                       Default: OFF
                                                           Display Group: L

          Parameters:

               ON   TNC will accept packets with invalid CRCs.

               OFF  TNC will only accept packets with valid CRCs.

          This  command causes  the TNC  to display  packets received  with
          invalid CRC fields.  Packets are accepted for display despite CRC
          errors if they consist  of an even multiple  of 8 bits and up  to
          339 bytes.   The TNC will attempt to decode the address field and
          display the callsign(s) in  the standard monitor format, followed
          by the text of the packet.

          This  mode is not normally enabled, since rejection of any packet
          with  an invalid CRC field  is what insures  that received packet
          data is error-free.   This mode  might be  enabled for testing  a
          marginal  RF  link  or   during  operation  under  other  unusual
          circumstances.

          If you set PASSALL  ON and monitor a moderately noisy channel you
          will  periodically see  "packets" displayed  in this  mode, since
          there is no basis for distinguishing actual packets received with
          errors from random noise.

          Logging of  stations heard  (for display  by MHEARD)  is disabled
          whenever  PASSALL  is ON,  since  the callsigns  detected  may be
          incorrect.


          RECONNECT call1 [VIA call2[,call3...,call9]]
                                                        Display Group: NONE

          Parameters:

               call1     Callsign of TNC to be reconnected to.

               call2     Optional  callsign(s) of  TNC(s) to  be digipeated
                         through.   As many  as eight  digipeater addresses
                         may be specified.

          RECONNECT is an immediate command.  It may be used  to change the
          path through which you  are currently connected to a station.  It
          may  only be  used  when your  TNC is  connected  on the  current
          stream.




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          REDISPLA n                                  Default: $12 <CTRL-R>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This command  is used to change the  redisplay-line input editing
          character.   The parameter n is  the ASCII code for the character
          you want to type  in order to  redisplay the current input  line.
          You can enter the code in either hex or decimal.

          You can type this character to cause the TNC to retype a line you
          have  begun.   When you  type the  redisplay-line  character, the
          following  things  happen:     First,  type-in  flow  control  is
          temporarily released  (if  it was  enabled).   This displays  any
          incoming packets that are pending.  Then a <BACKSLASH>  character
          is typed,  and the  line you  have begun is  retyped on  the next
          line.  If you  have deleted and retyped any characters,  only the
          final form  of the  line will  be shown.   You  are now ready  to
          continue typing where you left off.

          You can use the redisplay-line character to see a "clean" copy of
          your input  if you  are using  a printing  terminal and  you have
          deleted characters.  If  you have set BKONDEL OFF,  deletions are
          designated with <BACKSLASH> characters,  rather than by trying to
          correct the input line  display.  The redisplayed line  will show
          the corrected text.

          You can  also use this character  if you are typing  a message in
          Converse Mode  and a packet comes  in.  You can  see the incoming
          message  before you  send  your packet,  without concealing  your
          input.


          RESET
                                                        Display Group: NONE

          This is an  immediate command.  It  sets all parameters  to their
          default settings and re-initializes the TNC.

          WARNING:  All parameter  customizing  and monitor  lists will  be
          lost.

          If you want to  re-initialize the TNC using the  parameter values
          in battery  backed-up RAM, you  should turn  the TNC off  then on
          again, or issue the RESTART command.




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          RESPTIME n                                             Default: 0
                                                           Display Group: T

          Parameters:

               n         0 - 250, specifying 100 ms intervals.

          This  command sets  a minimum  delay that  is imposed  on acknow-
          ledgment packets.  This  delay may run concurrently with  default
          wait set by DWAIT and any random wait in effect.

          This  delay can be used to  increase throughput during operations
          such  as file  transfer when  the sending  TNC usually  sends the
          maximum number of full-length packets.  Occasionally, the sending
          TNC may  not have a packet ready  in time to prevent transmission
          from  being  stopped  temporarily,   with  the  result  that  the
          acknowledgment of earlier packets  collides with the final packet
          of the  series.  If the  receiving TNC sets RESPTIME  to 10, say,
          these collisions will be avoided.

          When  using priority  acknowledgment  (see ACKPRIOR),  this value
          must be set to 0 for proper operation.





























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          RESTART
                                                        Display Group: NONE

          RESTART is an immediate command.  It re-initializes the TNC using
          the defaults stored in bbRAM.  The effect of this  command is the
          same as turning the TNC OFF then ON again.

          RESTART  does not cause a reset of  the parameters in bbRAM.  See
          also the RESET command.


          RETRY n                                               Default: 10
                                                           Display Group: L

          Parameter:

               n         0 -  15, specifying  the maximum number  of packet
                         retries.

          The AX.25  protocol allows  for retries, i.e.,  retransmission of
          frames that  are not acknowledged.   Frames are  re-transmitted n
          times  before the operation is aborted.  The time between retries
          is specified by the command FRACK.   A value of 0 for n specifies
          an infinite number of retries.   If the number of retries exceeds
          n, the TNC will go to the disconnected state (with an informative
          message if not in Transparent Mode).  See also the FRACK command.

























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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          RXBLOCK ON|OFF                                       Default: OFF
                                                           Display Group: A

          Parameters:

               ON   The  TNC will  send  data to  the  terminal in  RXBLOCK
                    format.

               OFF  The TNC  will send  data to  the  terminal in  standard
                    format.


          RXBLOCK  is designed  for  automated operations,  such as  packet
          bulletin board stations.   It  is intended to  help such  systems
          discriminate between data received from the connected station and
          TNC-generated messages.

          Correct operation  of RXBLOCK is dependent on the AWLEN parameter
          being  set  to 8  (bits)  since the  character FF  hex  marks the
          beginning of a received data unit header.

          When RXBLOCK  is on, data from  other stations will  be sent from
          the TNC in the following format:

             ------------------------------------------------------
            |  $FF   |  L0  |  L1  |  PID  |       DATA            |
             ------------------------------------------------------

            (prefix) (length)         (pid)             (data)

          The fields above are defined as follows:

          prefix    $FF       ::= A character with all 8 bits set
          length    L0        ::= The high order length of the data,
                                  length, and pid fields logically ORed
                                  with the value $F0
                    L1        ::= The low order length of the data, length,
                                  and pid fields
          pid       PID       ::= The Protocol IDentifier byte received for
                                  the following data field
          data      DATA      ::=[Optional], variable length data


          For best  operation it is suggested that  parameters like AUTOLF,
          MFILTER, etc. be set OFF in order to prevent uncertainties in the
          size of the data field.





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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          RXCAL
                                                        Display Group: NONE

          RXCAL is an immediate command.  It is used for  precise alignment
          of the demodulator.   Briefly, after the modulator tones  are set
          using the  normal CALIBRATE routines, analog  loopback is entered
          and RXCAL  issued.  You then  tune the demodulator until  the CON
          and STA LEDs are both lit, or slowly alternate.   See the section
          Modem Calibration using CAL  and RXCAL for details on  using this
          command with a TAPR TNC 2.


          SCREENLN n                                             Default: 0
                                                           Display Group: A

          Parameters:

               n         0 - 255, specifying the screen or platen width, in
                         characters, of the terminal.

          This  value  is  used to  format  terminal  output.  A <CR>  <LF>
          sequence is  sent to the terminal at the end of a line in Command
          and Converse Modes when  n characters have been printed.  A value
          of zero inhibits this action.

          If your  computer automatically formats output  lines, you should
          set SCREENLN 0 to avoid a conflict between the two line formats.
























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          SENDPAC n                                       Default: $0D <CR>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This command selects the character that will force a packet to be
          sent in Converse Mode.  The parameter n is the ASCII code for the
          character  you want to  type in order  to force your  input to be
          packetized and queued for  transmission.  You can enter  the code
          in either hex or decimal.

          For ordinary conversation,  you will probably set SENDPAC $0D and
          CR ON.   This causes packets to be set  at natural intervals, and
          causes the <CR> to be included in the packet.

          If you  have set CPACTIME  ON, you  will probably set  SENDPAC to
          some value not ordinarily  used (say, <CTRL-A>), and set  CR OFF.
          This will allow  you to force  packets to be  sent, but will  not
          result in extra <CR> characters being transmitted in the text.






























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          SLOTS n                                                Default: 3
                                                           Display Group: L

          Parameters:

               n         0-127

          SLOTS specifies the number  of "slots" from which to  choose when
          deciding to access the channel.  For example, SLOTS 3 means there
          are three slots, each having a probability of 1/3 to be selected.
          Each slot  is DEADTIME long.  If SLOTS 0  is chosen, the TNC will
          act as if SLOTS 1 had been selected.

          Other  implementations  of  this   idea  of  channel  access  use
          "PERSISTENCE" to  decide the  probability of channel  access when
          the channel is clear and "PPERSISTENCE" to enable or disable this
          feature.

          A low value  means a greater  chance of  attempting to send  data
          when the channel is clear, and a higher value  means less chance.
          Normal  AX.25 practice  is  to have  every  station jump  on  the
          channel  when it  goes clear,  virtually assuring  collisions and
          retries.

          SLOTS  and  its  relation  to the  more  common  PPERSISTENCE and
          PERSISTENCE commands are given below:

          SLOTS     PPERSISTENCE   PERSISTENCE    Probability to XMIT

             1      OFF            255            Jump on = 100%
             2      ON             127            50%
             3      ON             85             33%
             4      ON             63             25%
             5      ON             51             20%

          and so forth.

          A  typical value would be 2  or 3 for a channel  with a few other
          users and 5 to 7 for  a fairly busy channel.  Higher  values than
          about  10 imply  the channel  is too  busy and  other frequencies
          should be used if available.

          Note:  SLOTS is independent of ACKPRIOR.








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          START n                                     Default: $11 <CTRL-Q>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This command selects the User Restart character, which is used to
          restart output  from the TNC  to the terminal  after it  has been
          halted by typing the User Stop character.  You can enter the code
          in either hex or decimal.

          The User Stop character is set by the STOP command.

          If  the User  Restart and User  Stop characters  are set  to $00,
          software  flow control to the  TNC is disabled,  and the TNC will
          only respond to hardware flow control (CTS).

          If the  same character is used for both the User Restart and User
          Stop  characters   the  TNC  will  alternately   start  and  stop
          transmission upon receipt of the character.


          STATUS
                                                        Display Group: NONE

          STATUS is  an immediate  command.   It  returns the  acknowledged
          status  of the  current  outgoing packet  link  buffer.   If  all
          outgoing packets are acknowledged, STATUS returns 'No Outstanding
          packets', otherwise it returns the 'Outstanding packets' message.
          Note  that  this  command   works  independently  of  the  RS-232
          flow-control state of the TNC.

          This  command may be useful for special applications, like if you
          can't see the STATUS LED on the TNC, or you want your computer to
          watch the status...















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          STOP n                                      Default: $13 <CTRL-S>
                                                           Display Group: C

          Parameters:

               n         0 - $7F, specifying an ASCII character code.

          This  command selects the User  Stop character, which  is used to
          stop output from the TNC to the terminal.  You can enter the code
          in either hex or decimal.  This is the character you will type to
          halt the TNC's typing so that you can read text before it scrolls
          off your display.

          Output is restarted with the User Restart character, which is set
          by the START command.

          If  the User  Restart and  User Stop  characters are set  to $00,
          software flow  control to the TNC  is disabled, and the  TNC will
          only respond to hardware flow control (CTS).

          If the same character is used  for both the User Restart and User
          Stop  characters   the  TNC  will  alternately   start  and  stop
          transmission upon receipt of the character.




























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          STREAMCA ON|OFF                                      Default: OFF
                                                           Display Group: C

          Parameters:

               ON   Callsign of other station displayed.

               OFF  Callsign of other station not displayed.

          This  command is used to  enable the display  of the connected-to
          station after the stream identifier.  This is particularly useful
          when operating with multiple connections allowed.  It is somewhat
          analogous to  the use of  MRPT to  show digipeat paths  when mon-
          itoring.

          In the example below, the characters inserted by enabling STREAM-
          CAll are shown in bold face type.

               |A:K4NTA:hi howie
               hello ted how goes it?
               |B:WA7GXD:*** CONNECTED to WA7GXD
               |Bmust be a dx record. ge lyle
               |Aunreal ted! fl-az no digis!
               |B:WA7GXD:big band opening...ge

          etc.

          The  same sequence with STREAMCAll  OFF would look  like the fol-
          lowing:


               |Ahi howie
               hello ted how goes it?
               |B*** CONNECTED to WA7GXD
               |Bmust be a dx record. ge lyle
               |Aunreal ted! fl-az no digis!
               |Bbig band opening...ge

          etc.

          Thus,  what  would   have  looked  like   "|B"  now  appears   as
          "|B:<callsign>:".  This option is very useful for human operators
          trying to operate multiple simultaneous connections.   It is pro-
          bably less useful for "host" operations.

          Note that, in the first example, the STREAMSWitch characters "|A"
          and  "|B" with no ":" after them  were entered by the operator of
          the  TNC to switch streams  for his multiple-connect  QSO(s).  If
          you  intend to operate multiple connections (as opposed to having


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          your "host"  computer operate multiple connections),  use of this
          option is recommended.


          STREAMDB ON|OFF                                      Default: OFF
                                                           Display Group: C

          Parameters:

               ON   Double all received STREAMSWitch characters.

               OFF  Do not "double" received STREAMSWitch characters.

          This command is used  to display received STREAMSWitch characters
          by "doubling" them.  The example below illustrates this action.

          With STREAMDB  on, and  STREAMSWitch  set to  "|", the  following
          might be displayed from your TNC:

               || this is a test.

          In this case the sending station actually transmitted

               | this is a test.

          The same frame received with STREAMDB OFF would be displayed as:

               | this is a test.

          When  operating with  multiple  connections, this  is useful  for
          differentiating  between  STREAMSWitch  characters received  from
          other stations and  STREAMSWitch characters internally  generated
          by your TNC.

          Note:  The  STREAMSWitch character must NOT be one  of the stream
          letters (A - J) for this command to function properly.















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          STREAMSW n                                     Default: $7C < | >
                                                           Display Group: C

          Parameters:

               n         0  - $FF,  usually specifying  an ASCII  character
                         code.

          This  command selects the character used  by both the TNC and the
          user that a new "stream" (connection channel) is being addressed.

          The character  can be PASSed in  CONVERS mode.  It  is always ig-
          nored  as a user-initiated stream switch in TRANSPARENT mode, and
          flows through as data.   This means that the outgoing stream  can
          not  be changed  while "on  line" in  TRANSPARENT mode  (you must
          escape to COMMAND mode to switch streams).

          For  further  usage  of this  character,  see  the  STREAMDBL and
          STREAMCA commands.
































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          TRACE ON|OFF                                         Default: OFF
                                                           Display Group: L

          Parameters:

               ON   Trace mode is enabled.

               OFF  Trace mode is disabled.

          This command is  used to enable the  protocol debugging function.
          When TRACE  is ON, all received frames will be displayed in their
          entirety, including all header  information.  In normal operation
          you  will probably never need this function; however, if you need
          to report an apparent software  bug, you may be asked to  provide
          trace information if possible.

          A  trace  display will  appear in  four  columns on  an 80-column
          display.  Following is an example trace display.  For comparison,
          the  frame shown  in  the trace  example  would be  monitored  as
          follows:

               KV7B>CQ,KF7B*:this is a test message

          The trace display would look like this:


      byte  ------------hex display------------ -shifted ASCII-- -----ASCII------
      000:  86A24040 40406096 AC6E8440 4060968C CQ  0KV7B  0KF   ..@@@@`..n.@@`..
      010:  6E844040 E103F074 68697320 69732061 7B  P.x:449.49.0  n.@@...this is a
      020:  20746573 74206D65 73736167 650D     .:29:.6299032.     test message.



          The byte column shows the offset into the packet of the beginning
          byte of the line.  The hex display column shows the next 16 bytes
          of the packet, exactly as received, in standard  hex format.  The
          shifted ASCII column attempts to decode the high order seven bits
          of  each byte  as  an ASCII  character  code.   The  ASCII column
          attempts to  decode the low order  seven bits of each  byte as an
          ASCII character code.   In a standard AX.25 packet,  the callsign
          address field will  be displayed correctly  in the shifted  ASCII
          column.  A text message will be displayed correctly  in the ASCII
          column.    Non-printing  characters and  control  characters  are
          displayed  in both ASCII fields as ".".   You can examine the hex
          display field to see  the contents of the sub-station ID byte and
          the control bytes  used by  the protocol.   Protocol details  are
          discussed in Chapter 9.




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          TRANS
                                                        Display Group: NONE

          This  is an immediate  command.  It  causes the TNC  to exit from
          Command  Mode into Transparent Mode.   The current  link state is
          not affected.

          Transparent Mode is primarily useful for computer communications.
          In  this  mode,  the "human  interface"  features  such  as input
          editing capability, echoing of input characters, and type-in flow
          control are disabled.   You may find Transparent Mode  useful for
          computer  Bulletin Board operations  or for transferring non-text
          files.  See the discussion of Transparent Mode in Chapter 5.


          TRFLOW ON|OFF                                        Default: OFF
                                                           Display Group: A

          Parameters:

               ON   Software flow  control can be enabled  for the computer
                    or terminal in Transparent Mode.

               OFF  Software flow  control is disabled for  the computer or
                    terminal in Transparent Mode. 

          If  TRFLOW is  ON, the  settings of  START and  STOP are  used to
          determine the type  of flow control used in Transparent Mode.  If
          TRFLOW is OFF,  only hardware  flow control is  available to  the
          computer  and all characters received by  the TNC are transmitted
          as data.  If  START and STOP are  set to $00, disabling  the User
          Stop  and User  Restart  characters, hardware  flow control  must
          always be used by the computer.

          If TRFLOW is  ON, and START and STOP are  non-zero, software flow
          control is enabled for the user's computer or  terminal.  The TNC
          will respond  to the  User's Restart  and User's  Stop characters
          (set  by START and STOP) while remaining transparent to all other
          characters from the  terminal.   Unless TXFLOW is  also ON,  only
          hardware flow control is  available to the TNC to  control output
          from the terminal.










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          TRIES n                                             Default: None
                                                           Display Group: L

          Parameters:

               n         0 -15,  specifying the current RETRY  level on the
                         currently selected input stream.

          This command is used to retrieve (or force) the  count of "tries"
          on the currently selected input stream.

          When used with no  argument: if the TNC has an outstanding unack-
          nowledged frame, it will  return the current number of  tries; if
          the TNC has  no outstanding unacknowledged frames, it will return
          the  number of tries required to obtain an acknowledgment for the
          previous frame.

          Note:  If  RETRY is  set to 0,  the value returned  by issuing  a
          TRIES command will always be 0.

          This command  is useful for  obtaining statistics on  the perfor-
          mance of a given path or channel.  It should be especially useful
          for automatic optimizing  of such parameters  as PACLEN and  MAX-
          FRAME by computer-operated  stations, such  as automatic  message
          forwarding stations  using less-than-optimum  paths (noisy HF  or
          satellite channels, for example).

          When  used with an argument, TRIES will force the "tries" counter
          to  the entered value.  Use of this  command to force a new count
          of tries is not recommended.





















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          TXDELAY n                                             Default: 33
                                                           Display Group: T

          Parameters:

               n         0 - 120, specifying 10 ms intervals.

          This value tells  the TNC how  long to wait  after keying up  the
          transmitter before sending data.   Some startup time is  required
          by all transmitters to put a signal on the  air;  some need more,
          some need less.   In general, crystal controlled rigs  with diode
          antenna  switching don't  need much  time, synthesized  rigs need
          time for PLL  lockup, and  rigs with mechanical  T/R relays  will
          need time for physical relay  movement.  The correct value for  a
          particular  rig should  be  determined by  experimentation.   The
          proper  setting of  this  value  may  also  be  affected  by  the
          requirements  of  the station  you  are communicating  with.   In
          general, TXDELAY should be set to the same value as DEADTIME when
          ACKPRIOR is ON.

          A TAPR TNC  1 running version 3.x firmware interprets  n in 40 ms
          intervals.   The value of TXDELAY  on TNC 2 will thus  be 4 times
          the value used by a TNC 1 to give the same delay time.




























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          TXDELAYC n                                             Default: 2
                                                           Display Group: T

          Parameters:

               n         0-120  specifying  additional transmit  delay time
                         added to TXdelay in terms of CHARACTER TIME at the
                         current radio port data rate.  Flags will be  sent
                         during this time, so a value of 1 is required as a
                         minimum.

          TXDELAYC is  used to fine-tune  transmit delay  after a  transmit
          command is issued  and before data is sent.   Used in conjunction
          with TXDELAY, it allows a link to be set for maximum performance.

          TXDELAY should be used to account for the time it takes the radio
          (the slower of  this TNC's radio and  the remote TNC's  radio) to
          switch  between  receive and  transmit  and  allow the  receiving
          unit's data carrier detect (DCD) circuitry to respond.  "0" bytes
          are  sent to  allow  the remote  TNC to  synchronize to  the data
          stream sent during TXDELAY.

          TXDELAYC  then sends flags to start the  frame.  If TXDELAYC 0 is
          selected, the TNC will act as if TXDELAYC 1 had been chosen.

          With this method of keying up, a user may operate at various HDLC
          data rates without having to reset TXDELAY if the same radios are
          used.  The  summation of TXDELAY and  TXDELAYC will automatically
          adjust the keyup time for the varying rates.


          TXDIDDLE ON|OFF                                       Default: ON

          The TNC sends NRZI 0s during TXDELAY/TXDELAYC intervals if TXDID-
          DLE is ON, and 7EH flags when it is OFF.  TXDIDDLE should be kept
          ON  unless you  are  certain the  TNCs  in your  network  require
          lengthy flagging intervals.

          A few 1.1.7 users (TXDIDDLE was  forced to ON in 1.1.7)  reported
          problems with other TNCs  that require flags during TXDELAY/TXDE-
          LAYC for carrier detection.  Now when  this problem crops up, the
          user  has   the  ability  to   turn  TXDIDDLE  OFF   and  restore
          connectivity.








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          TXFLOW ON|OFF                                        Default: OFF
                                                           Display Group: A

          Parameters:

               ON   Software flow  control can  be enabled  for the  TNC in
                    Transparent Mode.

               OFF  Software  flow  control  is  disabled for  the  TNC  in
                    Transparent Mode.

          If TXFLOW  is ON, the setting  of XFLOW is used  to determine the
          type of flow control used in Transparent Mode.  If TXFLOW is OFF,
          the TNC will use only hardware flow control and all  data sent to
          the terminal remains fully transparent.

          If TXFLOW and  XFLOW are ON, the TNC will use the TNC Restart and
          TNC Stop characters  (set by XON and XOFF) to  control input from
          the  terminal.   Unless  TRFLOW is  also  ON, only  hardware flow
          control  is  available to  the  computer or  terminal  to control
          output from the TNC.

          Note  that if the TNC Restart and  TNC Stop characters are set to
          $00, hardware flow control will  always be selected regardless of
          the setting of TXFLOW.


























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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          TXUIFRAM ON|OFF                                      Default: OFF
                                                           Display Group: L

          Parameters:

               ON   The TNC will "flush its buffers" to the radio port upon
                    loss of a connection.

               OFF  The  TNC  will  only  send  BEACON  and  ID  frames  as
                    unconnected (UI) frames.   It will discard  information
                    in its buffers upon loss of a connection.

          This  command  determines  whether  the TNC  will  transmit  most
          unconnected information packets.

          Setting  TXUIFRAMe  OFF  will  prevent  all  but  BEACON  and  ID
          unconnected ("UI") frames from being  originated and transmitted.
          This is  most useful  for BBS  and other  stations which  tend to
          leave  unacknowledged data  in  the TNC  transmit  buffer when  a
          connection is lost.  The normal behavior of a TNC  would send the
          buffered data as "UI" frames, adding to channel congestion.

          The  behavior  with  TXUIframe   OFF  serves  to  reduce  channel
          congestion because the now-useless data is never sent.

          Note:  TXUIFRAM  has no effect  on the digipeating of  UI frames.
          It only affects frames being originated at this station.


          UNPROTO call1 [VIA call2[,call3...,call9]]          Default: "CQ"
                                                           Display Group: I

          Parameters:

               call1     Callsign to be placed in the TO address field.

               call 2 - 9 Optional digipeater call list, up to eight calls.

          This  command is used to set the digipeat and destination address
          fields  of packets  sent  in the  unconnected (unprotocol)  mode.
          Unconnected packets are  sent as unsequenced  I (UI) frames  with
          the  destination and  digipeat  fields taken  from call1  through
          call9  options.   When no  destination is  specified, unconnected
          packets are sent to CQ.  Unconnected packets sent from other TNCs
          can  be monitored by setting  MONITOR ON and  setting BUDLIST and
          LCALLS  appropriately.   The  digipeater list  is  also used  for
          BEACON packets (which are sent to destination address BEACON).




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          USERS n                                                Default: 1
                                                           Display Group: L

          Parameters:

               n         0 -  10, specifying  the number of  active connec-
                         tions that may be established to this TNC by other
                         TNCs.

          USERS affects only the manner  in which incoming connect requests
          are  handled, and  has no  effect on  the  number or  handling of
          connections you may initiate with this TNC.

          For example,

             USERS 0   allows incoming connections on any free stream
             USERS 1   allows incoming connections on stream A only
             USERS 2   allows incoming connections on streams A & B
             USERS 3   allows incoming connections on streams A, B & C

          and so on through USERS 10.


          XFLOW ON|OFF                                          Default: ON
                                                           Display Group: A

          Parameters:

               ON   XON/XOFF flow control is enabled.

               OFF  XON/XOFF  flow  control is  disabled and  hardware flow
                    control is enabled.

          If XFLOW is ON, the computer or terminal is assumed to respond to
          the TNC  Restart and TNC Stop characters set by XON and XOFF.  If
          XFLOW  is OFF, the TNC will communicate flow control commands via
          RTS.














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          XMITOK ON|OFF                                         Default: ON
                                                           Display Group: L

          Parameters:

               ON   Transmit functions are enabled.

               OFF  Transmit functions are disabled.

          When  XMITOK  is  OFF,  transmitting is  inhibited.    All  other
          functions  of the  TNC remain the  same. In other  words, the TNC
          generates  and sends packets as  requested, but does  not key the
          radio PTT line.

          You might  use this  command  to insure  that your  TNC does  not
          transmit in your  absence if  you leave it  operating to  monitor
          packet activity.  This command can also be used for testing using
          loopback  or direct  wire connections  when PTT operation  is not
          relevant.
































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          XOFF n                                      Default: $13 <CTRL-S>
                                                           Display Group: C

          Parameters:

               n         0 to $7F, specifying an ASCII character code.

          This command selects the  TNC Stop character, which is  sent from
          the  TNC to  the  computer or  terminal to  stop input  from that
          device.  You can enter the code in either hex or decimal.

          This  character would ordinarily be set  to <CTRL-S> for computer
          data transfers.  If you are  operating your station in a Converse
          Mode and  there is some chance  that you might fill  up the TNC's
          buffers, you  might set this  character to <CTRL-G>  ($07), which
          rings a bell on many terminals. 


          XON n                                       Default: $11 <CTRL-Q>
                                                           Display Group: C

          Parameters:

               n         0 to $7F, specifying an ASCII character code.

          This  command selects  the TNC Restart  character, which  is sent
          from  the TNC to the  computer or terminal  to restart input from
          that device.  You can enter the code in either hex or decimal.

          This  character would ordinarily be set  to <CTRL-Q> for computer
          data  transfers.  If you are  operating your station in  Converse
          Mode,  and there is some chance that  you might fill up the TNC's
          buffers, you  might set this  character to <CTRL-G>  ($07), which
          rings a bell on many terminals.

















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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Messages

          This  section describes the messages your TNC may produce and the
          circumstances under which they will appear.

          General Messages

          |A

          Tucson Amateur Packet Radio TNC 2
          AX.25 Level 2 Version 2.0
          Release n.n.n mm/dd/yy - nnK RAM
          Checksum $xx
          cmd:

          This  is the sign-on message  that appears when  you turn on your
          TNC or when you issue the RESET command.  The release number will
          be updated whenever  the firmware is changed.  The  checksum is a
          hex number  which you  can compare  against the  correct checksum
          given for the firmware version you are using.

               NOTE:   The |A may display as a vertical bar and any capital
          letter from "A" through "J".

          bbRAM loaded with defaults

          This  message appears along with the sign-on message above if the
          battery  backed-up RAM  checksum  verification fails  at power-on
          time,  causing the TNC to  load the default  parameters from ROM.
          (This will be the case the first time you turn on your TNC.)

          This  message also  appears  if the  TNC  loads the  defaults  in
          response to the RESET command.

          cmd:

          This is  the Command Mode prompt.   When this prompt appears, the
          TNC is waiting  for you to  issue a command.   Anything you  type
          after this prompt  will be interpreted as  a command to  the TNC.
          If a monitored  packet has been displayed, the prompt  may not be
          visible,  even though you are in Command  Mode.  You can type the
          redisplay-line character (set by REDISPLA) to retype the prompt.

          was

          Whenever you change the  setting of one of the  TNC's parameters,
          the previous value will be displayed.  This confirms that the TNC
          properly interpreted  your command, and  reminds you of  what you
          have done.


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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          too many packets outstanding

          This  message will  appear  in response  to  a CONVERS  or  TRANS
          command, if you  have previously entered packet data  filling the
          outgoing buffer  in Converse  Mode or  Transparent Mode and  then
          returned to Command  Mode.  You will  be allowed to  exit Command
          Mode   after  some   of  the   packets  have   been  successfully
          transmitted.


          Command Mode Error Messages

          If  you make  a mistake  typing a  command to  the TNC,  an error
          message will  be  printed.   You  may see  any of  the  following
          messages depending on the type of error you have made.

          ?bad

          You typed a command  correctly, but the remainder of  the command
          line couldn't be interpreted.

          ?call

          You  entered a  callsign argument  that does  not meet  the TNC's
          requirements  for callsigns.   A  callsign may  be any  string of
          numbers and letters, including at least one letter.   Punctuation
          and spaces are not  allowed.  The sub-station ID,  if given, must
          be a (decimal) number from 0 to  15, separated from the call by a
          hyphen.

          ?clock not set

          This message appears if  you give the command DAYTIME  to display
          the  date  and  time  without having  previously  set  the clock.
          DAYTIME   sets  the  clock  if  it  is  given  with  the  daytime
          parameters, and displays the date and time if it is given without
          parameters.

          ?EH

          The  first  word  you  typed  is  not  a  command  or  a  command
          abbreviation.

          ?not enough

          You  didn't give  enough  arguments for  a  command that  expects
          several parameters.




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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          ?not while connected

          You attempted to change  MYCALL or AX25L2V2 while in  a connected
          or connecting state.

          ?not while disconnected

          You attempted to perform an operation that can only be done while
          connected.  This message  may appear when issuing a  RECONNECT or
          CONPERM command.


          ?already connected to that station

          The  multi-connect software will not permit you to connect to the
          same station using multiple streams.


          ?range

          A numeric argument for a command was too large.

          ?too long

          You  entered too long  a command line, and  the line was ignored.
          This might  happen, for example, if  you try to enter  too long a
          message  with BTEXT  or  CTEXT.   If  you get  this  message, the
          previous text entry was not changed.

          ?too many

               You  gave  too many  arguments  for a  command  that expects
          several  parameters.   For  example, MFILTER  can  have up  to  4
          arguments.

                    cmd:MFILTER $1B,$0C,$1A,$03,$07
                    ?too many

          ?VIA

          This  message appears  if  you attempt  to  enter more  than  one
          callsign  for the  CONNECT or  UNPROTO commands  without the  VIA
          keyword.


          Link Status Messages

          These messages inform you of the status of AX.25 connections your
          TNC  may be  involved in.   You can  always interrogate  the link
          status  by giving the CONNECT command without parameters.  If you

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          attempt a connection  when your  TNC is not  in the  disconnected
          state, the  TNC will  display the  link status  but will  take no
          other action.  The  following messages appear in response  to the
          CONNECT command.

          Link state is: CONNECTED to call1
                                          [VIA call2[,call3...,call9]]

          This  display shows the station your  TNC is connected to and the
          digipeater  route  if any.   The  callsign  sequence is  the same
          sequence you would enter to initiate the connection.

          *** LINK OUT OF ORDER, possible data loss
                                        [optional daytime stamp]

          This message is issued upon failure of a CONPERMed link.

          Link state is: DISCONNECTED

          No  connection  currently  exists.   You  may  issue the  CONNECT
          command to initiate a connection.

          Link state is: CONNECT in progress

          You  have issued a  connect request, but  the acknowledgment from
          the other station has not been received.  If you issue a DISCONNE
          command, the connect process will be aborted.

          Link state is: DISCONNECT in progress

          You have issued a disconnect request, but the acknowledgment from
          the  other station has not been received.   If you issue a second
          DISCONNE command, the TNC will go immediately to the disconnected
          state.

















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          Link state is: FRMR in progress

          The  TNC is connected  but a protocol  error has  occurred.  This
          should  never  happen  when two  TAPR  TNCs  are  connected.   An
          improper implementation  of the  AX.25 protocol could  cause this
          state  to be  entered.   The TNC  will attempt  to re-synchronize
          frame  numbers  with  the  TNC  on  the  other  end,  although  a
          disconnect  may result. Connects are not legal in this state, and
          a disconnect command will start the disconnect process.

          The TNC  will inform you whenever  the link status  changes.  The
          link status may change in response  to a command you give the TNC
          (CONNECT  or DISCONNE),  a connect  or disconnect  request packet
          from another station, a  disconnect due to the retry  count being
          exceeded, an automatic time-out disconnect (CHECK), or a protocol
          error.

          *** CONNECTED to: call1 [VIA call2[,call3...,call9]]

          This message appears when the TNC goes from the "disconnected" or
          "connect  in  progress"  state  to  the  connected  state.    The
          connection may be a result of a CONNECT command you issued, or of
          a connect request packet received from another station.

          *** connect request:call1 [VIA call2[,call3...,call9]]

          This  message  indicates  that the  TNC  has  received  a connect
          request from another station which it has not accepted.  This can
          happen if you have set CONOK OFF or if you  are already connected
          to another station.   When  the TNC  types this  message it  also
          sends a DM packet (busy signal) to the station that initiated the
          connect  request.  If the  TNC rejects a  connect request because
          you have  set CONOK OFF,  you can issue  your own request  to the
          station that called.

          *** DISCONNECTED

          This  message  is  displayed   whenever  the  TNC  goes   to  the
          disconnected state from any  other link state.  This  message may
          be  preceded  by   a  message  explaining  the  reason   for  the
          disconnect, below.










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          *** retry count exceeded
          *** DISCONNECTED

          This message is  given if the  disconnect was caused  by a  retry
          failure  rather  than by  a disconnect  request  from one  of the
          stations.   It will  also occur  if you  issue  two (2)  DISCONNE
          commands before the remote TNC responds to the first one.

          *** <callsign> busy
          *** DISCONNECTED

          This message indicates that your connect request was  rejected by
          a  DM packet (busy  signal) from the  other station.   A TAPR TNC
          will reject a connect request if CONOK is OFF or if it is already
          connected  to another station (or other stations up to the number
          allowed by the USERS command).

          frmr frame just sent:
          FRMR sent: xxxxxx

          The TNC is connected, and a protocol error has occurred.  The TNC
          has sent a special FRMR packet to attempt to re-synchronize frame
          numbers  with the  TNC on the  other end.   The  string xxxxxx is
          replaced  with the  hex codes  for the  three bytes  sent in  the
          information part of the FRMR frame.  This message will not appear
          if your TNC is in Transparent Mode.

          FRMR rcvd:

          This message is followed by a display of the FRMR packet received
          in the  trace display format.   This format  is explained  in the
          TRACE command entry. This message will not appear if your TNC  is
          in Transparent Mode.


          Health Counters

          A number of counters have  been added to TNC 2.  All  of them are
          16 bits wide,  and are ALWAYS initialized to 0000  on power up or
          "RESTART".

          These  counters are  displayed  using the  HEALTH  option of  the
          DISPLAY command.

               o- ASYFRERR:   Increases  when a  character received  on the
                              serial  port has  a framing  error.   A large
                              count  may  indicate problems  in  the serial
                              link  between the  TNC  and  the computer  or
                              terminal.


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               o- ASYQOVER:   Increases  when the TNC's  async input buffer
                              overruns.  A  count greater than  0 indicates
                              the host computer  is not responding properly
                              to  flow control from the TNC.  It also means
                              that data have been  lost, so you should take
                              steps to  find out why this  is happening and
                              get it fixed!

               o- ASYRXOVR:   Increases when the  software does not service
                              the asynchronous receiver in time.  Indicates
                              data  from  the  user  to the  TNC  is  being
                              dropped.   This  error  counter should  never
                              become non-zero under supported data rates.

               o- BBFAILED:   Counts number of times  bbRAM checksum was in
                              error.

               o- DIGISENT:   Each frame  digipeated by this TNC causes the
                              counter to increase.

               o- HOVRERR:    Increases when HDLC  receiver is not serviced
                              rapidly  enough  and  data  is  lost.    This
                              counter   should   never  increment   at  any
                              supported data rate.

               o- HUNDRERR:   Increases  when the  HDLC transmitter  is not
                              serviced  rapidly  enough   and  frames   are
                              aborted.    This  counter  should   never  be
                              non-zero at any supported data rate.

               o- RCVDFRMR:   Increases  when  Frame   reject  frames   are
                              received from a connected station.

               o- RCVDIFRA:   Increases for  each reception  of an  I frame
                              from a connectee.

               o- RCVDREJ:    Increases for  each  reception of  an  REJect
                              frame from a connectee.

               o- RCVDRNR:    Increases  when  this  TNC  receives  an  RNR
                              frame.  A large count is normal.

               o- RCVDSABM:   Each received SABM frame addressed to the TNC
                              causes this counter to be increased by one.







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               o- RXABORT:    Increases  when an aborted  frame is received
                              from the HDLC  controller.  Large  counts are
                              not uncommon.

               o- RXCOUNT:    Increases  when  any frame  is  received with
                              good  CRC (or  any CRC  if PASSALL  is turned
                              on).

               o- RXERRORS:   Increments  each  time  a received  frame  is
                              thrown  out  due  to  it   being  too  short,
                              suffering  overrun(s),   or it  having  a bad
                              CRC.  Latter occurs only when CRC checking is
                              enabled (i.e. PASSALL is  OFF).  This counter
                              will  often  increment  in  the  presence  of
                              noise.

               o- RXLENERR:   Increases when a received frame  has a length
                              error and  indicates the TNC  has temporarily
                              become confused.  It may be a result of a bug
                              in the SIO  chip and  a count above  0 is  no
                              cause for alarm.

               o- RXRESYNC:   Indicates the  number of  times  the TNC  has
                              recovered  from  RXLENERR  conditions.     In
                              firmware prior to 1.1.7, the TNC would simply
                              hang until RESTARTed or RESET.

               o- SENTFRMR:   Increments each time a Frame reject frame  is
                              transmitted.

               o- SENTIFRA:   Increases  by one  each  time an  I frame  is
                              sent.

               o- SENTREJ:    Whenever a REJect frame is  transmitted, this
                              counter is incremented.

               o- SENTRNR:    Increases when this  TNC sends an  RNR frame.
                              This   is   useful   for    determining   the
                              effectiveness of the FIRMRNR routines.

               o- TXCOUNT:    Incremented  whenever  a  frame is  correctly
                              transmitted.

               o- TXQOVFLW:   Counts how many  times frames were  discarded
                              because  the  outgoing  frame queue  was  too
                              small.

               o- TXTMO: Counts  how many  times  as  the TNC  successfully
                         recovers from HDLC transmitter time-outs.


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          Chapter 7  HARDWARE



          This  chapter includes detailed  specifications and  a functional
          description of the hardware design of the TAPR TNC 2.


          TNC 2 Specifications

          Processor CMOS Z-80A

          Clocks    Processor  master  clock  input  frequency:  2.4576 MHz
                    jumper selectable  to 4.9152 MHz (requires  use of Z80B
                    CPU, Z80B SIO/0 and 200 nSec EPROMs).

                    User Port Clock: Switch selectable at 16x baud rate.


          Memory    All   memory   in  industry-standard   JEDEC  Byte-Wide
                    sockets.

                    Standard complement of ROM: 32k = 1 x 27C256

                    Standard complement of RAM: 32k = 1 x 43256

                    ROM  complement jumper  selectable  for  8k-, 16k-,  or
                    32k-byte  parts.  Memory can be expanded to 32k ROM and
                    32k RAM using currently available parts.

          Serial    Z8440   SIO/0   port   B   configured  as   UART   plus
                    low-Portpower TTL-to-RS-232C signal level interface.

                    Baud rates supported: 300, 1200, 2400, 4800 and 9600.

                    Standard female DB-25S (DCE) RS-232C connector.

          Modem          Input demodulation  filter: MF-10 switched-capaci-
                         tor filter permits use  with unmodified FM  trans-
                         ceivers.   Easily configured  for SSB via replace-
                         able DIP headers.

                    Demodulator:  XR2211  PLL   demodulator  circuit   plus
                    related  components to  receive  up to  1200 baud  1200
                    Hz/2200 Hz FSK modulation.

                    Modulator:  XR2206  modulator   circuit  plus   related
                    components to  produce 1200 baud 1200  Hz/2200 Hz phase
                    coherent FSK.


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                    All  important  passive  modem  components  mounted  on
                    plug-in  DIP  headers  for  ease  in  substitution  and
                    modification.

                    Built-in   modem   calibration   system   requires   no
                    additional equipment.

                    An  external  modem  may   be  attached  via  a  single
                    connector which completely bypasses the on-board modem.

                    Support  for an  external  modem  tuning  indicator  is
                    provided via a separate connector.

          bbRAM          Non-volatile  storage  of all  important operating
                         parameters  is  accomplished  by using  a  battery
                         backed-up system for the  entire 16k bytes of sys-
                         tem RAM.

          Protocol  AX.25 Level 2 is supported.  Pre-Version 2.0 support is
                    compatible with earlier TAPR TNCs running 3.x software.
                    Full support of Version 2.0 protocol is provided.  Full
                    duplex radio link operation is supported.

          Operating Command Mode: accepts commands via user port.
          Modes
                    Converse  Mode: accepts  digital  data,  transmits  and
                    receives  packets,  permits  terminal editing  features
                    (character  delete, line  delete, input  packet delete,
                    output packet  delete and redisplay input)  via special
                    characters trapped  by the TNC. Escape  to command mode
                    via special character or BREAK signal.  Optional use of
                    packet completion timer as in Transparent mode.

                    Transparent  Mode:  accepts  digital   data,  transmits
                    packets  via packet  completion  timer or  buffer  full
                    only, and receives packets.   No local editing features
                    permitted.  Escape to  command mode via specially timed
                    character sequence or BREAK signal.

          Power          +10 to +15 volts DC at less than 200 mA.
          Required

          General Description

          The TNC 2 is based on the Zilog Z80 (tm) family of microprocessor
          components.   All  parts  used  in  the  TNC  should  be  readily
          available to the Radio Amateur.

          Major  electronic  devices in  the  TNC  include  a CPU  (Central
          Processing Unit)  for  controlling  the TNC  and  a  SIO  (Serial

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          Input/Output) chip  for providing  serial interface ports  to the
          on-board  modem (which connects to your radio) and to the RS-232C
          serial  terminal  port  (which   connects  to  your  computer  or
          terminal).

          The  TNC also  includes two  types  of memory.    ROM (Read  Only
          Memory)  stores the program that  tells the TNC  how to implement
          the AX.25 protocol.  Battery backed-up RAM (Random Access Memory)
          provides  a scratch-pad  area  for  temporary  data  as  well  as
          non-volatile  storage  for  operating  parameters  such  as  your
          station call sign.   The battery back-up feature enables  the TNC
          to "remember" these values when power is off so you don't have to
          enter them every time you want to operate.

          Other integrated circuits are  used for functions including clock
          oscillator,  baud-rate  generator,  memory-space  decoder,  power
          supply and voltage  inverter, clock recovery, transmit  watch-dog
          timer  and modem.  Refer  to the schematic  diagram while reading
          the following circuit descriptions.


          Detailed Circuit Description

          Oscillator

          U10a, U10b, U10c, R46, R47, R48, C24, C47, C51, and Y1 provide an
          accurate crystal-controlled oscillator for system timing.

          R48  forces inverter U10a into  its linear region  and provides a
          load for crystal Y1.  C47 provides an adjustable reactive element
          to allow  the oscillator's  frequency to be  precisely set  (this
          precision  is not normally required).   Inverter U10c buffers the
          clock   for  additional   stability  before   driving  additional
          dividers.

          R46 is  used to bias  "HCT" logic to  the proper levels  for best
          oscillator operation; it is not necessary if U10 is an "HC" logic
          element.


          Dividers and Baud-rate Generator

          U10e, U10f, U4a, U4b,  U1, and SW2 provide clock  outputs derived
          from the  oscillator.  Only one of the first 5 switches (terminal
          baud rate)  and only one  of the last  3 switches (RF  baud rate)
          should be on at any time.

          Inverter  U10f  provides  buffering  and  isolation  between  the
          divide-by-two  output  of counter  U4a  and  the capacitive  load
          presented  by the CPU (U22) and the  SIO (U21).  U10f's input may

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          be  at 2.4576  MHz  (standard) or  4.9152  Mhz via  jumper  JMP2.
          Operation at the faster clock may require the use of higher-speed
          parts.  Capacitors C59 and C60 are used to slow the  edges of the
          outputs of  U4a, and capacitor C61 is used to slow the edges from
          U10f, helping to reduce RFI.

          Counter U1 is a multiple-stage divide-by-two circuit that divides
          the  signal at its input many times.   This allows you to select,
          via switch SW2, the desired signaling (baud) rate to  be used for
          your computer or terminal as well as the radio channel baud rate.

          The  output from counter U1 at pin  12 provides a real-time clock
          interval  signal for the SIO.   During normal  operation, the SIO
          will  be programmed to interrupt  the CPU on  every transition of
          this 600  Hz signal.  This interrupt  occurs 1200 times a second,
          and is used for protocol and calibration timing functions.

          Inverter U10e  buffers the radio  port "16x" baud-rate  signal in
          case it is routed, via modem disconnect J4 pins 11 and 12, to  an
          external modem.   If this buffer  were not included,  reflections
          from  the distant termination might cause  counter U1 to generate
          count errors.

          Counter U4b provides a properly scaled clock for the transmit NRZ
          to NRZI encoder (see Serial Interface, below).


          CPU Complex

          EPROM U23 provides system ROM for program storage.  Selector U12a
          acts as  a ROM decoder,  mapping the  ROM into  the CPU's  memory
          address space beginning at address 0.

          Static  RAM  U25 provide  system  RAM  for temporary  scratch-pad
          storage, message buffers, etc.   Also, because the RAM  is backed
          up by  a battery  and will  not lose its  contents when  the main
          power is removed, it is used to provide semi-permanent storage of
          user-supplied  information (such  as your  call sign).   Selector
          U12b acts as  a RAM address decoder, with RAM starting at address
          8000 hex.  JMP12 allows selection of 16k bytes (using 2 x 6264 8k
          RAMs) or 32k  bytes (using 1 x 43256 32k RAM))  of RAM  (only 32k
          bytes currently supported by TAPR firmware).

          The  sections of CMOS switch U13 are  used to insure that the RAM
          is not selected when  main power is removed.   This ensures  that
          the contents of the RAM are not accidentally scrambled as the CPU
          loses power; it also ensures that the RAM  is in the "power-down"
          state for minimum battery power consumption.



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          Serial Interface

          Serial  Input/Output (SIO)  device U21  provides two  channels of
          serial I/O.

          The B SIO channel is used for the computer or terminal interface.
          Operational amplifier sections U3a, U3b,  and U3d act as  RS-232C
          drivers  while Schmitt  trigger  inverters  U9a  and U9b  act  as
          RS-232C  receivers.    These  circuits consume  less  power  than
          conventional RS-232C drivers and receivers.

          The A SIO channel  is used for the  radio/modem interface and  is
          normally operated as a full duplex HDLC channel for compatibility
          with  the  AX.25 protocol  specification.   Latch  U5 and  ROM U6
          provide  a "state  machine"  for recovering  the  clock from  the
          received NRZI data.  The state machine also converts NRZI data to
          NRZ for the SIO.  Inverter U9c and flip-flop U11a  provide NRZ to
          NRZI conversion for the transmit side of the radio channel.  This
          conversion between NRZ formatted data  and NRZI formatted data is
          necessary because the AX.25  protocol specification requires NRZI
          operation while the SIO is only capable of NRZ.  Jumper JMP11 may
          be used  to bypass  the  NRZ -->  NRZI  conversion for  use  with
          external modems, if required.


          Watch-dog Timer

          Inverters U7c, U7d, U7e,  and Q10 provide a "watch-dog"  timer on
          the transmit key  line to  ensure that the  transmitter does  not
          remain keyed for  more than about  30 seconds  if the TNC  fails.
          This allows you to leave a station (such as  a remote digipeater)
          on-the-air  and  unattended  without  much  chance  of  having  a
          malfunction "lock up" the packet channel.  This also helps ensure
          compliance  with  FCC  regulations  regarding  unattended station
          operation.

          Jumper  JMP4  is provided  for testing  purposes.   When  JMP4 is
          installed,  timing  capacitor  C31  is   shunted,  disabling  the
          watch-dog timer.


          Modem

          U16,  an XR2206, is a Frequency Shift Keying (FSK) modulator that
          generates  an audio data signal for use by the radio transmitter.
          Two tones are  used, one for each digital level,  and these tones
          may  be calibrated via trimpots  R77 and R78  in conjunction with
          the on-board  calibration support  circuitry and software.   When
          the transmitter is not being keyed, transistor Q9 is switched on,
          thus preventing U16  from producing  tones.  This  allows you  to

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          leave a microphone connected to your packet transmitter for voice
          operation.  DIP header U15 contains  the three passive components
          which determine the operation  of the modulator, as well  as R83,
          the PTT watch-dog circuit timing resistor.

          R76 is used to set the tone output level to the transmitter.

          U20,  an   XR2211,  provides  a  Phase  Locked   Loop  (PLL)  FSK
          demodulator.   It  converts the  received audio FSK  signals into
          digital data  at standard logic levels.  This data is sent to the
          state machine clock  recovery and NRZI  to NRZ format  conversion
          circuits.    R79  is  used  to  calibrate  the PLL  demodulator's
          free-running  frequency which is set midway between the FSK tones
          being  received.   This  tone  is  measured  by  the  calibration
          software and the output signal produced by U8a and U8b,  which is
          a  frequency doubling shaping  circuit.  DIP  header U19 contains
          all  passive  components  which  determine the  behavior  of  the
          demodulator, with the exception of R73 and C45, the DCD detection
          filter.  These two components normally do  not need to be changed
          when the  modem is reconfigured.   However, in the  event the TNC
          will be dedicated to 300 baud operation, the DCD detection filter
          at U18  pin 3 should have its time constant increased by a factor
          of 4, by increasing C45.

          U18, an MF-10 switched capacitor filter, provides audio amplitude
          and phase equalization to shape the received audio signal  before
          it goes to the  XR2211 demodulator.  This equalization  helps the
          demodulator properly  process signals  by correcting some  of the
          distortion  that  many FM  radios  introduce.   By  replacing the
          components  on DIP header U17,  this filter may  be configured at
          will.


          Power Supply

          Regulator  Q3  and  associated   components  provide  a  +5  volt
          regulated output for the  TNC digital logic circuitry.   In order
          to reduce conducted  RFI from  the digital  power source,  series
          inductor L1 is provided.  Transistor Q4, in conjunction with CMOS
          inverters  in U14,  provides a  "power  failure" circuit  for the
          battery-backed  RAM  chips   to  ensure  that   RAM  is  in   the
          "power-down"  state when the main power is removed.  In addition,
          this circuit provides the main power-on reset signal via U7f.

          Transistors Q5 and Q6 are used to isolate the battery from the +5
          volt line when main power is available.  R33 protects the lithium
          battery from overload conditions  and provides a convenient means
          of monitoring battery current drain when the TNC is switched off.
          JMP5  provides a means  of disconnecting the  lithium battery for
          TNC 2 maintenance.

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          U2 and associated components  form a charge-pump voltage inverter
          which generates  an unregulated  negative supply for  the RS-232C
          drivers.

          U3c,  Q2,  CR6 and  surrounding  components  provide a  regulated
          source of -5 volts for the modem chips. 

          The modem  power sources  and  ground are  isolated from  digital
          logic switching noise by inductors L2 and L3.


          RS-232C Handshaking Protocol

          The  CTS, DSR and DTR lines of the RS-232C port (J1) are used for
          hardware  "handshaking"  protocol to  control  the  flow of  data
          between the terminal (DTE) and the TNC (DCE).

          The TNC  always asserts (makes true)  Data Set Ready (DSR)  on J1
          pin 6 via resistor R16.  Thus, whenever the TNC is powered up, it
          signals  to the  terminal  connected to  J1 that  the TNC  is "on
          line."

          The  terminal indicates it is ready to  receive data from the TNC
          by asserting its  Data Terminal  Ready (DTR) output,  J1 pin  20.
          The TNC  will send  data when  it has  data to  send  and DTR  is
          asserted.   If the  terminal  is not  ready to  receive data,  it
          should negate (make false) DTR to  the TNC.  Thus, data flow from
          the TNC to the terminal is controlled by the use of the DTR line.
          The state of the DTR line is ignored by the software if "software
          flow control" is enabled in this direction.

          The  TNC  asserts  its Clear  To  Send (CTS)  output,  J1  pin 5,
          whenever it is  ready to receive data from the  terminal.  If the
          TNC's buffers fill, it will negate CTS, signaling the terminal to
          stop  sending data.   The TNC  will assert  CTS when  it is again
          ready  to receive data  from the terminal.   Thus, data flow from
          the terminal to the TNC is controlled by the use of the CTS line.
          The CTS line  is always  asserted if "software  flow control"  is
          enabled in this direction.

          Some  serial  I/O  ports  do  not  implement  CTS,  DTR  and  DSR
          handshaking.  If  these pins  are not connected  at the  terminal
          end, they will  be pulled up (and thus  asserted) by resistors at
          the  TNC end.  However,  a non-standard serial  connector may use
          some  pins for  other  purposes, such  as  supplying power  to  a
          peripheral device, so be sure  that your system either implements
          the  CTS, DTR and  DSR handshake or  has no  connections to these
          pins   of  J1  whatsoever.    Note   that  reference  to  RS-232C
          "compatibility"  or the presence  of a DB-25  type connector does
          not guarantee that you have a full RS-232C serial port!

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          The TAPR TNC 2 supports most standard baud rates from 300 through
          9600. The port supports standard parity  options as well as 7- or
          8-bit character  lengths.   Setting these terminal  parameters is
          discussed in Chapter 4.

          If you  want to  interface your TNC  with a device  configured as
          DCE, such as a telephone modem  or another TNC, a so-called "null
          modem"  cable  may be  constructed  to interchange  the  data and
          handshake signals.   See for  example Byte, February,  1981, page
          198.


          Jumper Functions

          The following table lists the function of each jumper on  the TNC
          2  PC board.   The  default positions for  JMP7, JMP8,  JMP9, and
          JMP10 are necessary for normal operation to occur.

               Jumper    Position       Function

               JMP1      ON             !DCD (RS-232C) stays on
                         OFF (default)  !DCD reflects connect status

               JMP2      LEFT           4.92 MHz CPU clock
                         RIGHT (default)   2.46 MHz CPU clock

               JMP4      ON             disable Tx watch-dog
                         OFF (default)  enable Tx watch-dog

               JMP5      ON             Lithium battery connected
                         OFF (default)  Lithium battery disconnected

               JMP6      ON (default)   U23 is type 27256
                         OFF            U23 is not type 27256

               JMP7      ON             analog loopback mode
                         OFF (default)  normal modem operation

               JMP8      ON             demodulator enabled
                         OFF (default)  demodulator calibrate

               JMP9      TOP            calibrate U16 tones
                         MID            calibrate U20 tone
                         LOW            bypass state machine
                         OFF (default)  normal modem operation

               JMP10     ON             digital loopback mode
                         OFF (default)  normal modem operation



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               JMP11     LEFT                transmit data NRZ
                         RIGHT (default)     transmit data NRZI

               JMP12     TOP                 16k RAM (2 x 6264)
                         BOTTOM (default)    32k RAM (1 x 43256)


          Modem Disconnect - J4

          The modem disconnect, J4, on  the TNC 2 PC board is  provided for
          using  an external  modem  with  the TNC.    This allows  use  of
          higher-speed modems,  such as  9600 baud, or  more sophisticated,
          higher-performance modems for OSCAR or other uses.

          The  following information  is primarily  for those  who wish  to
          interface external modems to the TNC.  Familiarity with modem and
          serial data channel terms is assumed.

          A physical  connector for J4 is  not supplied with the  TNC.  Any
          standard 20-pin header for  use with IDC cable  connectors should
          work.   Suitable parts are the Ansley 609-2027, the 3M 3428-6202,
          etc.

          When installing the connector, be sure  to line up the marked pin
          (pin 1  ) of  the header  with the  lower edge  of  the PC  board
          nearest U21.  Cut the traces  on the bottom of the TNC  PC board,
          with  a sharp knife or  Moto-Tool, between each  pair of adjacent
          pins of J4.   To use the  on-board modem, install  push-on jumper
          links across these same pin pairs.

          The  signals used at connector  J4 are at  standard TTL interface
          levels.  A TTL  high, or 1, is greater  than +2.4 volts but  less
          than +5.25 volts.  A  TTL low, or 0,  is less than 0.8 volts  but
          greater  than -0.4 volts.  DO NOT  connect an RS-232C level modem
          directly to J4!

               NOTE: The modem disconnect is  similar, but not identical to
               that  used in TNC 1.   Be very  careful about interfacing an
               external modem using the same cabling you may  have prepared
               for use with TNC 1!  

          The connector pin-outs are as follows.









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          Pin 1     Carrier Detect Input

               This pin tells the SIO radio port that  a valid data carrier
               has been detected.  It should be pulled high when no carrier
               is  detected and low when  a carrier is  present.  This line
               must  be  implemented  unless  the  software  release  notes
               indicate otherwise.  It  is normally jumpered to pin  2 when
               the on-board modem is used.

          Pin 2     Carrier Detect Output

               This  pin is  an  output from  the  the on-board  modem  and
               satisfies  the requirements outlined for pin 1 above.  It is
               normally jumpered to pin 1 when the on-board modem is used.

          Pin 3     SIO Special Interrupt Input

               This signal is routed to the radio port DCD input pin on SIO
               U21.  This signal is normally used during modem calibration.
               It  may  also  be used  for  other  purposes;  if so,  these
               functions  will be  listed  in the  software release  notes.
               This pin is  normally jumpered  to pin 4  when the  on-board
               modem is used.

          Pin 4     SIO Special Interrupt Generator Output

               This signal  is an output  from the on-board  modem.  It  is
               normally used for modem calibration only.  If it is used for
               other functions, they will be stated in the software release
               notes.  This  pin is  normally jumpered  to pin  3 when  the
               on-board modem is used.

          Pin 5     SIO RTS Output

               This  signal is  used for transmitter  activation.   The SIO
               will  pull this output low  when the TNC  wants to transmit;
               otherwise  it  will  remain  high.   This  pin  is  normally
               jumpered to pin 6 when the on-board modem is used.

          Pin 6     Transmitter Key Input

               This signal is an input to the on-board modem.  It activates
               the  PTT pin of the radio connector via the watch-dog timer.
               It should be left high and pulled low only when transmission
               is desired.  This pin is normally jumpered to pin 5 when the
               on-board modem is used.

          Pin 7     CONNECT Status Output



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               This  pin is an output from the SIO.  It is normally low and
               goes high only when the TNC is in the connected (error-free)
               mode  with another packet station.   Its status is monitored
               via the CON LED.

          Pin 8     Unacknowledged Packets Pending Status Output

               This pin is an output from the SIO.  It  is normally low and
               goes high only when  this TNC has unacknowledged packets  in
               its  transmit buffer.  Its  status is monitored  via the STA
               LED.

          Pin 9     CTS Input

               This  pin is  an input  to the  SIO.   It is  high when  the
               attached modem is not ready to accept data, and low when the
               attached modem is  ready to accept data.   The TNC  will not
               attempt to  send data when  this pin is  high.  This  pin is
               normally jumpered to pin 10 when the on-board modem is used.

          Pin 10    Transmitter Key Input

               This pin is physically tied to pin  6, above.  It is used in
               conjunction with pin  9, above, to allow the TNC  to use the
               on-board modem whenever the transmitter is activated.

          Pin 11    Transmitter Clock (16x) Input

               This pin is tied to the NRZ-to-NRZI converter, which expects
               a clock signal at 16 times the desired radio port data rate,
               e.g.,  4800 Hz for 300 baud.   This pin is normally jumpered
               to pin 12 when the on-board modem is used.

          Pin 12    Transmitter Clock (16x) Output

               This pin is tied to the  radio baud rate switch network.  It
               provides a clock  at 16  times the desired  radio port  data
               rate.   This  pin is  normally jumpered to  pin 11  when the
               on-board modem is used.

          Pin 13    Receive Clock Input

               This  pin is tied  to the SIO  receive clock input  pin.  It
               expects a clock at the  desired data rate (1200 Hz  for 1200
               baud),  of the  proper  phase relationship  to the  received
               data.   This pin  is normally  jumpered to  pin 14  when the
               on-board modem is used.




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          Pin 14    Receive Clock Output

               This  pin is the received data clock signal derived from the
               NRZI-to-NRZ state machine.  This pin is normally jumpered to
               pin 13 when the on-board modem is used.

          Pin 15    TNC 2 Ground Reference

               This pin ties to the TNC digital ground system, at the SIO.

          Pin 16    No Connection

               This pin is unused.

          Pin 17    Receive Data Input

               This pin is the received data input to the NRZI-to-NRZ state
               machine.  This  pin is normally jumpered to pin  18 when the
               on-board modem is used.

          Pin 18    Receive Data Output

               This  pin provides  receive  data from  the on-board  modem.
               This  pin is normally jumpered  to pin 17  when the on-board
               modem is used.

          Pin 19    Transmit Data Output

               This line  is the  NRZ or  NRZI (depending  on the  state of
               JMP11) data output.  This pin is normally jumpered to pin 20
               when the on-board modem is used.

          Pin 20    Transmit Data Input

               This input line  accepts data  to be be  transmitted by  the
               modem.   This pin  is normally jumpered  to pin  19 when the
               on-board modem is used.


          If  you elect  to use  an off-board  modem, be  sure to  properly
          shield the interconnecting cables for RFI protection.


          Tuning Indicator Interface - J3

          In order to facilitate  communications on HF and OSCAR,  the TAPR
          TNC 2 includes a connector for attaching a tuning indicator.  The
          attached unit  may range from  an oscilloscope to  a specialized,
          LED-style  unit such as the  one described in  the June 1984 PSR.
          Refer to the Exar Application Note referenced in the Bibliography

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          for  details on functions of the XR2211 signals available on this
          connector.  A mating connector assembly (shell and 5 pins) may be
          obtained from TAPR.

          NOTE:       Exercise  caution  when  using  this connector.    Be
          especially  aware that the TNC 2 modem circuitry is referenced to
          +5 volts and -5 volts, not +12 volts and 0 volts!

          The connector pinouts are as follows.


          Pin 1     -5 volts (Common)

               This pin is the on-board  modem's analog common.  It is  not
               ground, but -5  volts.  This pin should not  be used to sink
               appreciable  currents or  excessive noise may  be introduced
               into the modem, reducing its performance.

          Pin 2     Loop Data Filter Output

               This pin is  connected to the output of  the XR2211 PLL data
               filter (U20 pin 8).  It is a high-impedance source, and care
               should be exercised  to ensure that no extraneous signals or
               low-impedance loads are attached.

          Pin 3     Demodulator Reference Voltage

          The  internal   XR2211  data  comparator   reference  voltage  is
          available on this pin.  By comparing this voltage with the signal
          on J3 pin 2, correct tuning  may be accomplished.  As above, this
          pin must be carefully  shielded from noise, and has  a relatively
          high internal impedance.

          Pin 4     Data Carrier Detect

               This pin is an open-collector output that goes near -5 volts
               (J3 pin 1) when valid data is not present.  It is  pulled to
               +5 volts by R74 when valid data is detected.

          Pin 5     +5 Volts

               This pin is  a source of +5 volts DC.  It should not be used
               to  source  more  than  a  few  milliamperes of  current  or
               degradation  of the on-board modem's weak-signal performance
               may result.






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          Chapter 8  TROUBLESHOOTING






          WARNING: Never remove or insert an IC with power on!

          Your  TAPR  TNC 2  is a  complex  piece of  electronic equipment.
          Servicing  must  be approached  in a  logical  manner.   The best
          preparation for troubleshooting is to study the detailed hardware
          description in  Chapter 7.  While  it is not possible  to present
          all possible problems, symptoms  and probable cures, this section
          of the manual will give direction to troubleshooting based on our
          experience.


          General Tests

          In most  cases  we  have  found that  careful  visual  inspection
          combined with simple measurements  generally reveals the problem.
          The  most useful single instrument  for troubleshooting is a good
          DVM that can read AC and DC volts, and can non-destructively test
          resistance while the ICs are still in their sockets.

          While  a number  of checks  may  be made  without the  aid of  an
          oscilloscope,  you will  need  one to  check  signals at  various
          points  on the board if you fail  to locate the problem by visual
          means or  with a meter.   Be very careful about  shorting pins on
          ICs when applying meter  or scope probes to  the board.  It  is a
          good  idea to attach a secure ground  lead to the meter or scope,
          one that won't accidentally short across components on the board.
          A good  place to pick  up this  ground is on  the threads of  the
          screw that mounts regulator Q3 to the printed-circuit board.


          Step 1:  Power Supply

          The first thing to check in  any malfunction is the power supply.
          Check  the  power supply  levels at  the  outputs of  the voltage
          regulators (Q2  and Q3) as  well as the   output of  the inverter
          (U2).  Are they close to their nominal values?  Do all the ICs in
          the suspected area have  the proper voltage on their  power pins?
          Is there excessive ripple in any of the DC voltage lines?  If so,
          check the  regulator and associated components, working backwards
          toward the  input  power switch.    If  the voltage  is  low,  in
          conjunction  with a hot regulator, suspect a short circuit on the
          board.


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          If the problem is in the -5 volt supply, work backwards from Q2's
          collector  (also  at  U16  pin  1),  which  should  be  -5  volts
          regulated, to the junction of C9 and CR2 (-V unregulated).  If no
          voltage appears at -V, then  U2 or a related component may  be at
          fault.    Verify that U2  is oscillating by  looking at the  wave
          form at U2 pin  5.  If -V is  more negative than -7  volts (i.e.,
          normal),  but the -5 volt  regulated voltage is  wrong, check the
          negative regulator components U3,  Q2, R5, R6, R7, R8,  CR6, C10,
          C11 and C158.  If  both -V and the -5 volt regulated  voltage are
          wrong, look for shorts.


          Step 2:  Obvious Problems

          Look for any unusual  physical symptoms.  Have you  installed any
          ICs the wrong way?  This is almost guaranteed to ruin  the IC and
          produce  a high current through  it, detectable by  the IC's high
          temperature.   Are  any  components discolored?   Does  something
          smell burnt?  Do any of the parts seems excessively warm?  If you
          have  never  had your  fingers  on  operating digital  integrated
          circuits before  you may erroneously  conclude they  are too  hot
          when  they are  actually operating  normally.   In  general their
          normal temperature will be well below the boiling point of water,
          but you may not want to keep your finger on them very long. 


          Step 3:  Assembly Problems

          Carefully  inspect the PC board and component installation.   Are
          any cold solder joints present?  (See the  soldering instructions
          in the TNC 2 Assembly Manual.)  Is  a metal screw shorting to the
          board anywhere?  Are all ICs firmly seated in their sockets?  Are
          any IC  leads tucked under the  chip or otherwise bent  in such a
          manner that they aren't making proper contact with the IC socket?
          (This is a very common error, accounting for most problems!)

          Inspect   the  diodes  and  electrolytic  capacitors  for  proper
          installation.  Are the  diode cathodes pointing the  correct way?
          Are the negative ends of the electrolytic capacitors pointing the
          correct way?


          Step 4:  Cabling Problems

          Inspect  the interconnection  cabling.   Does it work  on another
          TNC?  Has  the radio  and/or terminal been  successfully used  on
          packet with this or another TNC?  Are  all the connections tight?
          Has the cable frayed or broken?



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          Specific Symptoms

          While  the  steps  described  above  may  seem  obvious,  careful
          inspection  often will point  to the problem  or give significant
          clues as to the probable area of the TNC most suspect.  After the
          above inspection  has been completed and  apparent problems dealt
          with, it is time to proceed to more specific analysis.


          Symptom:  TNC appears dead

          If  the TNC  powers  up with  the  PWR, STA,  and  CON LEDs  lit,
          followed by STA  and CON extinguishing a second or  so later, the
          processor  is  working  and  the  software  is  probably  working
          correctly.  You should  suspect the terminal port at  this point.
          Check  all connections and  verify the logic  levels according to
          the terminal interface troubleshooting section in this chapter.

          Oscillator and Reset Circuits

          If no  LEDs wink during the  reset cycle the problem  may be more
          serious.  Check to see that the crystal oscillator is working and
          that  an "M1"  signal (154  kHz square  wave, 0  to +5  volts) is
          coming from  U22 pin  27.   The crystal  oscillator input  to the
          processor (U22)  is pin 6.  The input clock should be a (possibly
          distorted)  square wave signal.   Verify that the  clock input at
          pin 6  of U22 is  running at the  correct frequency (near  2.4576
          MHz).

          Verify that  the battery  backed-up RAM protection  circuit, com-
          posed of  Q4, U14 and associated devices, is going to +5 volts at
          U14 pin  6 after  input power is  applied.   This signal  enables
          normal operation of U24 and  U25.  There should be a  logical low
          on the output  of U7  pin 12 coincident  with the application  of
          power and lasting for  a few hundred milliseconds.   Without this
          RESET signal, the Z80 probably won't start up properly.

          Digital Logic Lines

          Remember  that all  the logic  circuits  operate at  standard TTL
          levels (a "low" is less than +0.8  V and a "high" is greater than
          +2.4 volts),  and all digital  inputs and outputs  switch between
          these  two  levels.   Thus, if  you  see logic  signals switching
          between 0 and, say,  1 volt, you can  be sure there is  a problem
          (usually  a short).  On the other  hand, do not mistake switching
          transients on digital logic lines for improper operation -- these
          show up as ringing and other distortions.

          Verify that there is  activity on the control bus  READ and WRITE
          lines, the 3 CHIP-ENABLE lines on the memories (U23-25, pins 20),

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          the IOREQ line on U21 pin 36, and  the INT line on pin 16.   Each
          of these  lines should show  activity, and  if any line  is quiet
          this is a sign of trouble.

          Logic lines that show no activity may often be traced  to a short
          on the pc board, probably due to a solder splash or bridge.

          Address and data line shorts may also show up as lack of activity
          on the control  bus lines,  especially the chip  selects.   Check
          each of the 16 address and 8  data lines for activity.  Any lines
          showing a lack of activity are not operating properly.

          If  you suspect problems with address or data lines, try removing
          all the memory chips.  Each address and data line will now show a
          distinct  pattern.    The   address  lines  should  be  (possibly
          distorted) square waves whose periods increase by a factor of two
          on successive lines as you step line by line from A0 to A15.

          If you  decide to use an ohmmeter to check for shorted lines, use
          a low voltage/low current test instrument.  (Most modern DVMs are
          fine for  this.)  If  in doubt, remove  any ICs connected  to the
          lines you  are measuring.  If you suspect a short, check the high
          density areas of the PC board for the problem.  In most cases the
          short will be found there.  It is very unlikely that the PC board
          itself will have a short, as every board shipped by TAPR has been
          electrically  tested  for  shorts   and  opens  on  a  commercial
          "bed-of-nails" board tester prior to acceptance by TAPR.


          Symptom:  Modem won't calibrate or key transmitter.

          Double  check the placement of parts on each DIP header assembly,
          measuring  resistor  values  and  checking  for   shorts  between
          adjacent components and for shorted capacitors.

          Calibration of the demodulator's 1700 Hz tone and the modulator's
          1200 Hz  and 2200 Hz  tones is  done in software  by setting  the
          specified  device  to  generate  the frequency  in  question  and
          routing the signal  to U21 pin 22  where it causes  interrupts to
          the Z80  microprocessor.   The software calibration  routine then
          examines the ratio between this interrupt rate  and a fixed  1200
          Hz interrupt  generated by a  600 Hz square  wave at U21  pin 29,
          then sets the STA and CON LEDs appropriately.  In the case of the
          1700  Hz  tone,  it  is first  passed  through  U8,  acting as  a
          frequency doubling  Schmitt trigger.   The  input  signal to  the
          Schmitt trigger  is a modified sawtooth wave.  In the case of the
          modulator, the signal presented to U21 pin 22 comes directly from
          U16 pin 11, and should be a reasonable square wave.



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          Troubleshooting  improper  calibration  amounts  to  checking for
          proper signals at  U21 and following up any improper  signal.  If
          the calibration  signal is  present, but you  cannot successfully
          calibrate the  frequency, you  may have an  out-of-spec frequency
          determining  component.   Check  the  values  of the  appropriate
          passive components.   Also, check the placement of jumpers!  As a
          last resort, check the signal frequency with a frequency counter.
          Note  that,  due  to   frequency  jitter  while  calibrating  the
          demodulator,  the STA and CON  LEDs may blink  somewhat even when
          the 1700 Hz demodulator frequency is correct.

          If  the  transmitter  doesn't key,  the  problem  may  be in  the
          watchdog timer, U7, or the PTT transistor, Q10.  Check especially
          for  an  open timing  capacitor C31  or  a bad  solder connection
          associated with R83 in header U15.


          Symptom:  Uncopyable transmitted or received packets

          If  no one seems able to  decode your packet transmissions, it is
          often  the case that your  transmitter is being  overdriven.  The
          solution is to reduce the drive level via trimpot R76.  Note that
          direct connection to typical microphone inputs requires R76 to be
          turned   to  near   the  minimum   signal  position   to  produce
          sufficiently low signal levels.

          If  you   are  having   problems  hearing  other   stations,  the
          demodulator circuitry associated with U20 may be at fault.  Check
          the  center  frequency of  the  VCO  in  U20  using the  1700  Hz
          calibration procedure.  Working  in the direction of flow  of the
          input  signal  from the  radio, verify  that  it is  being passed
          through to pin 2 of U20, the input pin.  The signal there  should
          be above 50 mV and below 3 V peak-to-peak for proper operation of
          the demodulator.  It  should be relatively clean, although  a few
          tens of millivolts of  noise is normal, and the  signal amplitude
          should  not change by  more than about  25% between  high and low
          tones.


          Terminal Interface Troubleshooting

          If you can't  get the TNC  to sign on  and accept data from  your
          terminal  or  computer,  the  problem  may  be   in  the  RS-232C
          interface.  The troubleshooting guide below is provided as an aid
          to help in resolving  problems that may be related to the RS-232C
          port.





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          Symptom:  TNC won't sign on to the terminal.

          If you find the TNC won't send data to your terminal,  one of the
          first things to do is to verify that the DTR line at pin 20 of J1
          is not  being held low.   If the software flow  control option is
          disabled, the TNC will not send  data to the terminal unless  its
          DTR is asserted.  If the terminal does not implement the  DTR/CTS
          protocol, the DTR/CTS lines  (pins 20 and 5 on J1)  should remain
          unconnected.

          Verify that  the voltages on the TNC are correct.   If the TNC is
          in otherwise good condition, check the following pins on the SIO,
          U21  (Z8440).   Pin  23 should  be TTL  low  (between 0  and +0.8
          volts).   If this  voltage is incorrect, check  the voltage at U9
          pin 3  and verify  that it  is greater  than +3  volts.   If this
          voltage is  correct, U9 or the traces  around it may be  bad.  If
          this is not  the problem,  disconnect the terminal  and check  it
          again.  If this doesn't help, U9, R20 or R22 may be at fault.

          If  the  above checks  are  ok, observe  pin  26 of  U21  with an
          oscilloscope  and cycle the power switch on the TNC.  Transitions
          on this  pin shortly after reset indicate that the TNC is sending
          data.  Verify that transitions are also  present on U3 pin 1.  If
          these tests fail, the fault could be with U13, R25, R26, U21, J1,
          the  attached cable  or  faulty soldering  (shorts, cold  joints,
          etc.)


          Symptom:  The TNC appears to be signing on but  only gibberish is
          printed on the terminal.

          This  indicates  that some  combination  of the  data  rate (baud
          rate), parity  option, or number of  start and stop  bits are not
          set  the same at the TNC  and at the terminal.   If possible, set
          your terminal to 300 baud.  Also verify that the  terminal is set
          for seven data bits, space parity, and 1 stop bit.  These are the
          default settings stored in EPROM.  For 300 baud, set DIP switch 1
          ON (up) and set  switches 2 through 5  OFF (down).  Be sure  only
          one of these 5 switches is up!  Perform a hard reset by the power
          switch  OFF then ON (out  then in).   The  sign on message should
          appear.

          If  the TNC still prints  gibberish, verify that  the terminal is
          set to 300 baud and do a power off  then on cycle on both the TNC
          and  terminal.    If  the  message  still  fails  to  appear  try
          troubleshooting with  an oscilloscope,  looking first at  the TXD
          pin  (pin 26)  of U21 (Z8440),  then at  the x16  baud rate clock
          (4800 Hz at 300 baud) on pin 27 of U21.



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          Symptom:  The TNC signs on OK but won't accept commands.

          After the TNC signs on, try giving it a command such as MYCALL or
          any other command.   If the  default settings are  in effect,  it
          will  attempt to echo each character you type back to the screen.
          If it doesn't  echo, be sure that U21 pin 23  has a voltage level
          between 0 and +0.8 volts on it.   The voltage on U9 pin 3  should
          be greater than  +3 volts.  If these voltages aren't correct, the
          fault  could be  in  U9, U21,  J1,  R20, R22,  soldering, or  the
          interconnecting cable.

          If the above checks  are OK, use an  oscilloscope to verify  that
          data is present on  U21 pin 28 and U9 pin 1 when you strike a key
          on your  terminal.   If  not, the  data isn't  getting from  your
          terminal to the TNC.  Check J1, the cable and U9 again.  Finally,
          be sure  that your terminal  actually uses levels  less than   -3
          volts  and greater  than +3 volts  for signal  levels.   0 and +5
          volts may not work, especially if they are being used direct from
          a computer.  For  example, the Commodore 64 uses TTL  levels that
          will work  only if they  are inverted!   This is  because RS-232C
          logic polarity definitions are opposite those of TTL.






























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          Chapter 9  PACKET RADIO PROTOCOL


          Explanation of Protocol

          The material in this chapter is intended to supply an overview of
          the  protocol  used  to  transmit  data  by  the  TAPR  software.
          References  are given  to more  detailed information  required by
          those  wishing to  implement these  protocols on  other hardware.
          The material presented  below is somewhat tutorial  in nature for
          those  who  have not  had  previous exposure  to  layered network
          protocols,   but   it   presumes   some   knowledge  of   general
          communications  hardware  and  software.   Persons  already  well
          versed in networking may want  to skip this chapter and refer  to
          the  primary defining  document, Amateur  Packet-Radio Link-Layer
          Protocol,  AX.25 Version 2.0,  available from the  ARRL, 225 Main
          Street,  Newington, CT  06111  ($8.00 US, postpaid  in the United
          States as of this writing).

          The TAPR TNC hardware  and software architecture is  organized in
          accordance  with the  International Standards  Organization (ISO)
          layered network model.   The model describes seven levels  and is
          officially  known  as the  ISO  Reference Model  of  Open Systems
          Interconnection, or simply  the ISO  Model.  The  model and  many
          other interesting  topics are  discussed in Computer  Networks by
          Andrew S. Tanenbaum.

          The ISO  model provides for  layered processes, each  supplying a
          set  of  services to  a  higher  level  process.   The  TAPR  TNC
          currently implements the first two layers, the Physical layer and
          the Data Link layer.


               Physical Layer

          The duty of the Physical Layer,  layer one, is to provide for the
          transmission and  reception of  data  at the  bit level.   It  is
          concerned only with how each bit is physically transmitted, i.e.,
          voltages on a hardwire line or modem tones on phone or RF links.

          The physical layer  of the TAPR  TNC is  described in Chapter  7,
          Hardware.   It  is  compatible with  the  various TNCs  currently
          available to  radio  Amateurs.   The  actual modem  interface  is
          compatible with the  Bell 202  standard which is  similar to  the
          CCITT  V.23  standard.    Any  other  hardware  device  which  is
          compatible with the  Bell 202 standard should  be compatible with
          the TAPR TNC, at least at level one of the ISO reference model.




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          Data Link Layer

          The duty of the Data Link layer is to supply an error-free stream
          of data to higher levels.  Since level one simply passes any bits
          received  to level two and is unaware of the content or overlying
          structure of the data, transmission  errors are not detectable at
          level one.  Level two carries the responsibility of detecting and
          rejecting bad  data, retransmitting rejected data,  and detecting
          the reception of duplicate data.

          Level  two  accomplishes this  task  by partitioning  data  to be
          transferred by  level one into  individual frames, each  with its
          own error detection  field and frame identification fields.   The
          TAPR TNC  supports  two  versions of  a  level-two  layer,  AX.25
          version 1.0 and  AX.25 version 2.0.   Each of these  protocols is
          based on HDLC, the High-Level Data Link  Control protocol defined
          by the ISO.


          HDLC Frames

          Exact  knowledge of  the  format of  HDLC  frames has  been  made
          largely unnecessary by  the advent of LSI and VLSI communications
          chips  which interface directly with the level one hardware.  The
          level  two  software need  only supply  data  to fill  in various
          fields and the  chip takes care  of the rest.   For  completeness
          however, an HDLC frame looks like this:

             | FLAG | ADDRESS | CONTROL | PID & DATA | FCS | FLAG |

          FLAG  A unique bit sequence (01111110) used to detect frame boun-
          daries.  A technique  called "bit stuffing"  is used to keep  all
          other parts of the frame from looking like a flag.

          ADDRESSA  field  normally  specifying  the  destination  address.
          AX.25  uses a  minimum of  14  bytes and  a maximum  of 70  bytes
          containing the actual call signs  of the source, destination, and
          optionally up to eight digipeaters.

          CONTROLA  byte which  identifies the  frame type.   In  the AX.25
          protocol, the control field  may include frame numbers in  one or
          two 3-bit fields.

          PID         A Protocol Identification  byte appears as  the first
          byte  of the  HDLC  DATA field  in  AX.25 Level  Two  information
          frames, and identifies which Level  3 protocol is implemented, if
          any.  In the case where no Level 3 protocol is implemented, PID =
          $F0.



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          DATA   This  field   contains  the   actual  information   to  be
          transferred.  This  field need not be present.   Most frames used
          only for link control do not have data fields.

          FCS Frame Check Sequence, a 16-bit error detection field.

          The communications chip recognizes  the opening and closing flags
          and passes the address, control, and data (including PID)  fields
          to  the software.    The FCS  field  is  a Frame  Check  Sequence
          computed by the  transmitting chip and sent with  the frame.  The
          receiving  chip recomputes the FCS based on the data received and
          rejects  any frames in which the received  FCS does not match the
          computed FCS.  There is virtually  no chance of an undetected bad
          frame  using this method.   This satisfies the  level two task of
          bad data detection.

          The communications  chip used in the  TAPR TNC 2 is  a Zilog 8440
          SIO  operating in  conjunction  with a  two-chip "state  machine"
          which is used to recover the data clock.  The transmitted data is
          encoded  in  NRZI  form,  which  encodes  a  "0"  data bit  as  a
          transition in  the encoded bit  stream and a  "1" data bit  as no
          transition.   This, in combination with  the "bit-stuffing" which
          ensures that  no more than five  "1"s occur in a  row except when
          FLAG  bytes are being transmitted, guarantees that  a logic level
          transition  occurs  at  least once  every  5  bit  times.   These
          frequent transitions allow the  receiver to synchronize its clock
          with  the transmitter.  Other chips which are compatible with the
          SIO  + "state machine" are the Western Digital 1933/1935 (used on
          the TAPR TNC  1, AEA  PKT-1, Heathkit HD-4040,  etc.), the  Intel
          8273 (used on the VADCG and  Ashby TNCs) and the Zilog 8530 (used
          on the Xerox 820 FAD adapter).

          While the  HDLC format  supplied by  the communications  chips is
          used by the  AX.25 protocol,  there are several  other Layer  Two
          concerns.   These are  duplicate frame detection,  connection and
          disconnection of  the level  two layers  on  different TNCs,  and
          buffer  overrun  avoidance.    The AX.25  protocol  solves  these
          problems as described below.


          AX.25 Level Two

          AX.25  is based on the  Balanced Link Access  Procedure (LAPB) of
          the  CCITT X.25  standard.   LAPB in  turn  conforms to  the HDLC
          standard.  Two  extensions are made to LAPB in  AX.25.  These are
          the extended  address field, and the  unnumbered information (UI)
          frame.  In LAPB, addresses are limited to eight bits, while AX.25
          uses from 112 to 560 bits, containing the originator's call sign,
          the  destination call sign and  an optional list  of one to eight
          digipeater (simplex digital repeater) call signs.

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          The UI frame  is used  to send information  bypassing the  normal
          flow control and  acknowledgment protocol.  The UI frame  is  not
          acknowledged  but can be transmitted at layer two without fear of
          disturbing  higher layers.   It  is used  for beacon  frames, for
          automatic  identification  packets, and  for  sending information
          frames when the TNC is not connected to another TNC, e.g., CQ and
          QST activities.

          The  exact specifications  for AX.25  are supplied  in   the ARRL
          publication  Amateur  Packet-Radio  Link-Layer   Protocol,  AX.25
          Version 2.0.   The TAPR implementation  adheres to this  standard
          for  AX.25 version  2.0.   The implementation  of version  1.0 is
          almost identical to  the TAPR TNC 1 version of  AX.25 protocol in
          software  releases 3.x.    This provides  compatibility with  the
          majority of Amateur packet radio stations.

          The  following  table lists  the frame  types  used by  AX.25 and
          describes their purpose.   This  material is provided  to give  a
          general understanding  of the  protocol, and  is not  intended to
          replace the published specification.   The byte fields  are given
          as they appear  in memory after data is  received, i.e., the high
          order bit is at  the left and the low order bit  is at the right.
          This is  also the  format of  the display  provided by the  TRACE
          command.  Some texts, including the AX.25 protocol specification,
          list the bits in the  order in which they are transmitted,  which
          is low order bit first.

          The control bytes  are presented in hex with "x" used to indicate
          four bits which depend on the acknowledge functions the packet is
          performing.  Usually  "x" is a frame  number.  Frame numbers  fit
          into  three bits and are used  to ensure that frames are received
          in order  and that no frames  are missed.  Since  only three bits
          are available, the frame number is counted modulo 8.  This is why
          the MAXFRAME parameter  has a  ceiling of 7:  no more than  seven
          frames can be "in flight" (transmitted but unacknowledged) at one
          time.   A short  description of  the use of  the frames  is given
          after the table.


                        Table 9-1.  AX.25 Control Codes

              Code   Abbrv         Frame Type

               x1    RR            Receive Ready
               x5    RNR           Receive Not Ready
               x9    REJ           Reject
               03    UI            Unnumbered Information
               0F    DM            Disconnected mode
               2F    SABM          Connect request
               43    DISC          Disconnect request

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               63    UA            Unnumbered Acknowledge
               87    FRMR          Frame reject
               even   I             Any frame ending in an even number (in-
          cluding $A, $C, and $E) is an information frame.


          I    This  and UI frames are the only frame types containing user
               data.  The control byte contains this frame's number and the
               number  of the next frame  expected to be  received from the
               other end of the link.

          RR   Usually  used to acknowledge receipt of an  I frame.  The RR
               function can also be performed by sending an I frame with an
               updated "expected next frame number" field.

          RNR  Used when the buffer space on the receiving side is full.

          REJ  Used to request retransmission  of frames starting from "x".
               Missed  frames  are detected  by  receiving  a frame  number
               different from that expected.

          DM   Sent  in response to any frame received other than a connect
               request (SABM)  when  the  TNC is  disconnected.    Sent  in
               response to an SABM whenever the TNC is on the air but can't
               connect  to the requesting user, e.g., if the TNC is already
               connected to someone else or if CONOK is OFF.

          SABM Set Asynchronous Balanced Mode - initiates a connect.

          DISC Initiates a disconnect.

          UA   Sent to acknowledge receipt of an SABM or DISC.


          FRMR Sent when an abnormal condition occurs, i.e., the control
               byte received is undefined or not proper protocol at the
               time received.
          UI   An I frame without a frame number.  It is not acknowledged.


          Channel Use and Timing Functions

          The following discussions mention timing parameters which are set
          by various  commands.  These timing functions  are also discussed
          in Chapter 5.

          An  important part of  any packet radio protocol  is the means by
          which many stations make  efficient use of an RF  channel, achie-
          ving maximum throughput with minimum interference.  The basis for


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          this time domain multiplexing   is Carrier-Sensed Multiple Access
          (CSMA) with collision detection and collision avoidance.

          CSMA means simply that  (as every Amateur knows) no  station will
          transmit if the frequency  is in use.  The  TNC continually moni-
          tors for the presence of an  audio data carrier on frequency  and
          transmits only  if there is no carrier.   (The  RF carrier is not
          normally  detected; however, an input  is available on  the TNC 2
          radio  interface connector to allow such  an input.)  In order to
          make detection of a busy channel more reliable, the TNC sends  an
          audio signal (continuous flags) any time the transmitter is keyed
          and  a packet is not being sent,  as during the transmitter keyup
          delay  (TXDELAY), or while a  slow audio repeater  is being keyed
          (AXDELAY).

          By itself, CSMA is not  enough to insure a minimum, or  even low,
          interference rate, due to the likelihood of simultaneous keyup by
          two  or more  stations.   This is  where collision  detection and
          collision avoidance come in.  The TNC  detects a collision by the
          absence  of  an ACK  from  the station  it  is sending  to.   The
          receiving station  does not  acknowledge the frame  that suffered
          the collision, since either  the FCS was incorrect or  the packet
          was  not heard.  There are other possible reasons for non-receipt
          of the packet, but the TNC's  response is based on the assumption
          of a collision.  

          After transmitting  a packet, the TNC waits a "reasonable" length
          of  time   (FRACK)  for  an  acknowledgment.     "Reasonable"  is
          determined by the link activity, frame length, whether the packet
          is being digipeated, and  other time-related factors.  If  no ACK
          is received,  the packet must  be re-sent.  If  the unACKed frame
          was  lost due to a collision, the  assumption is that there is at
          least one other packet station  out there that also lost  a frame
          and  will probably have  exactly the same  criterion for deciding
          when to retry the transmission as this station is using.

          In order  to avoid  a second  collision, the  collision avoidance
          protocol calls for the stations retrying  transmissions to wait a
          random  time interval  after hearing  the frequency  become clear
          before they  key  their  transmitters.    There  must  be  enough
          different random wait times to provide a reasonable chance of two
          or  more stations  selecting  different values.   The  difference
          between  adjacent time values must  be similar to  the keyup time
          delay  of typical  stations on the  frequency.  This  is the time
          lapse after  a station keys its transmitter before other stations
          detect its  presence on  the channel,  and is  a function  of the
          keying circuitry of the transmitter and the signal detection cir-
          cuitry of the receiver.   We have chosen the random time to  be a
          multiple  (0-15)  of  the  transmitting  station's  keyup   delay


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          (TXDELAY).   This  is  reasonable if  one's  own keyup  delay  is
          similar to that of other stations on the channel.

          One other factor  must be taken into consideration  in optimizing
          data  throughput.    The  currently  implemented  link  protocols
          provide   for   relaying   (digipeating)   of   packets.      The
          acknowledgment  procedure  for such  packets  is  that the  relay
          station  simply repeats  packets  without  acknowledgment to  the
          sending  station.    The receiving  station  sends  its  ACK back
          through the same  digipeaters to the originating  station.  Since
          the digipeated packets are not acknowledged to the digipeater, an
          unsuccessful transmission   must be  retried from scratch  by the
          originating station.   In order to help alleviate  the congestion
          of the  frequency that  tends to  result when digipeated  packets
          suffer  collisions, the  digipeater is  given first  shot at  the
          frequency every time it becomesclear.  Other stations, instead of
          transmitting as soon  as they hear the channel clear, must wait a
          short  time (DWAIT).   This  restriction applies to  all stations
          except  the digipeater,  which is  permitted to  transmit relayed
          packets  immediately.    This prevents  digipeated  packets  from
          suffering collisions  except on transmission  by the  originating
          station.

          A special time delay (RESPTIME) is  used as the minimum wait time
          prior  to  transmitting  acknowledgment frames,  to  prevent TNCs
          accepting data  at high  speed  from the  asynchronous port  from
          colliding  with acknowledgment  frames when  fewer than  MAXFRAME
          packets are outstanding.  The receiving TNC will wait long enough
          before sending the ACK so that it will hear the data packet which
          would have caused the collision, thus avoiding a  fairly frequent
          source of delay in versions of AX.25 prior to 2.0.


          Channel Flow Control

          Flow control of data through  the link is determined by the  rate
          at which data  is being supplied  to a sending  TNC and  accepted
          from a receiving TNC.

          A TNC receiving data from the link will send an RNR when the next
          I  frame successfully received will  not fit into  the buffer for
          output to the serial port.

          Whenever a TNC  transmitting data received  from the serial  port
          over the link runs out of temporary buffer space, the serial port
          will be halted by an  XOFF character or CTS signal.  In the TNC 2
          implementation this  happens whenever  there are 7  packets built
          and less than  210 characters left  in the buffer for  input from
          the serial port.


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          When the TNC receiving data from the link clears out its buffers,
          it sends  an RR  to  the transmitting  TNC.   In  order to  guard
          against  the  possibility  of the  RR  being  lost  and the  link
          becoming   permanently   locked,   the   transmitting   TNC  will
          periodically  re-transmit the packet that  provoked the RNR.  The
          receiving  TNC will  continue to  respond with  RNR until  it can
          accept the packet.












































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          Appendix A  Multi-Connect Survival Guide

          This  section  is  a  very  brief  tutorial  on the  use  of  the
          multiple-connection  capability  included   with  this   software
          release.

          Why Multi-Connect?

          Multiple connection capability is a powerful addition to your TNC
          2.    It is  very useful  for  traffic net  operation, multi-user
          bulletin boards, path checking and so forth.

          What is Multi-Connect?

          Multiple  connection  operation  is  not the  same  as  multi-way
          operation.   With  multiple  connect, you  may establish  several
          point-to-point "links" with  various stations.  Multi-way,  which
          is  not   available,  would   enable  multiple  stations   to  be
          simultaneously  interconnected to each  other, with  each station
          seeing all data passed from any station in the group, error free.

          Multiple  connection operation  is another  step  on the  road to
          proper  networking,  and   networking  should  eventually   allow
          multi-way operation.

          What Commands Set my TNC 2 to Normal Operation?

          Your  TNC 2  defaults the  multi-connect-related commands  to the
          following parameters:

               CONPERM   OFF
               STREAMCAll     OFF
               STREAMDouBLe   OFF
               STREAMSWitch   |
               USERS          1

          This sets up your TNC 2 to act just like a "normal" TNC does that
          doesn't support multiple connections.  The  key to obtaining this
          traditional operation is to set USERS 1.

          How Do I Invoke Multi-Connect?

          If USERS  is not 1,  you are  telling the TNC  to allow  multiple
          connections to  your stations from other stations.   In addition,
          TRANSPARENT mode will operate  differently, in that incoming data
          will  be prefixed  with  the current  STREAMSWitch character  and
          identifier  (such as  "|A").   Thus,  truly transparent  multiple
          connection operation is not possible with this software release.



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          The  STREAMSWitch character, defaulted to "|", should be set to a
          character you won't normally  use.  Note that this  character may
          be set to a hex value between $80 and $FF.  This may allow you to
          use  8-bit characters (AWLEN 8)  if your terminal  or computer is
          capable of generating such  "characters." This could help prevent
          confusion in  interpreting incoming  data from other  stations if
          they happen to send data that includes your selected STREAMSWitch
          character.

          Although  not  foolproof, enabling  STREAMDBL  may  also help  in
          sorting out STREAMSWitch characters included in the received data
          from a valid stream switches generated by your TNC 2.

          STREAMCAll should be especially helpful when manually operating a
          station in which you allow multiple connections.

          When in CONVERSE  mode, you  may switch streams  by entering  the
          STREAMSWitch  character  (default  "|"),  followed  by  a  stream
          identifier  ("A" through "J"), followed  by the data  you wish to
          send  to the  station on  that stream.   See  the example  in the
          description of STREAMCAll for an illustration of this.

          If  all this seems a bit confusing,  don't worry, it is! The only
          way to really understand multiple connect operation is to try it!
          Once you have your  TNC 2 on-the-air, and have  gained confidence
          in  "normal"  packet operation,  try setting  USERS  2 and  get a
          couple of friends to connect to you.  Play with the commands (you
          can't  hurt the  TNC by  issuing commands  to it!) and  see their
          effects.

          Happy packeting! 




















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          Appendix B  Prioritized Acknowledgment - An Overview

          THE IDEA

          The idea behind the prioritized acknowledgement (PriACK) protocol
          is quite simple.   Acknowledgments (ACKs) get  priority access to
          the channel so that time is not wasted retrying packets that have
          already been correctly copied by the remote TNC.  In normal AX.25
          practice, for a variety of reasons, the ACK is often not received
          within the time limit defined by the FRACK (T1) protocol timer.

          In fact, because "channel access" methods are not clearly defined
          in the AX.25 Level Two Version 2.0 protocol document, the present
          protocol   is  more   likely   to  synchronize   collisions  with
          acknowledgement packets than with any other type of packet!

          THE PROBLEM

          When a channel becomes clear, if your  TNC has something to send,
          it will immediately send it.  Unfortunately, if anyone else's TNC
          has something to send, it will also "jump on" the channel as soon
          as it becomes clear.  The result is collisions and retries.  Only
          after a collision  does the present protocol suggest using random
          backoff.   Thus, an acknowledgment  to a just-received  packet is
          almost assured  of a  collision-and-retry sequence, even  thought
          the TNC correctly received  the packet.  This will  usually cause
          the TNC  which is awaiting  the ACK to  time out and  re-send the
          data.

          To  this  collision synchronization  mechanism,  AX.25 Level  Two
          Version 2.0  adds a propensity  to cause even ACKs  which are not
          from hidden terminals, and thus less susceptible to collision, to
          be delayed  beyond even  generous FRACK  timer settings  when the
          channel gets busy.

          Once  FRACK times out,  even if the ACK  finally makes it through
          before  the retry is sent, the original packet is retried anyway.
          This wastes a lot of time which could be better used clearing the
          channel of some of the legitimate offered load.

          This feature of AX.25 Level Two protocol accounts for much of the
          abysmal performance  of the  currently popular NETROM  and THENET
          nodes when used with omnidirectional antennas systems.

          HOW IT WORKS

          PriACK protocol avoids the above problems by giving ACKs priority
          access to the channel.  It does this in such a way that even ACKs
          coming  from   hidden  terminals  are   usually  protected   from
          collision.

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          Standard AX.25 protocol gives a  limited version of this priority
          access only to digipeated frames through the DWAIT timer.  

          Ack  prioritization  works with  slotted  channel  access in  the
          following way:

          1.   Response  frames (ACKs)  are  always sent  immediately  upon
          receipt of a  valid packet.   Ultimately,  not even  DCD will  be
          checked for  sending an ACK.   However, in this  release DCD will
          still hold an ACK off the channel.

          2.   Stations queued up to  access the channel but  waiting for a
          channel  busy condition (DCD true) to clear, will start a slotted
          access procedure only after  enough time for a response  frame to
          clear the channel has transpired (ACKTIME).  This is true even if
          the  TNC waiting  to use  the channel cannot  hear the  ACK being
          sent.

          3.  Slot time  windows (DEADTIME) are set large enough  to ensure
          the local TNC  will be  able to accurately  determine if  another
          detectable  station   has  started  transmitting   in  any   slot
          preceeding the slot selected by the local TNC.  This prevents two
          TNCs which have selected adjacent slots from colliding.

          As you  can  see, under  this  protocol  there will  never  be  a
          condition  where an  ACK is  delayed from  being sent  beyond the
          FRACK timer limitation.  However, the FRACK timer is still active
          and must be  set to a value that is long enough to allow time for
          (MAXFRAME * PACLEN) + ACKWAIT to  expire before FRACK does.  This
          time will depend on the radio and radio channel data rate in use.
          The TNC  knows that if  it doesn't see  the ACK  immediately when
          expected, it is probably never going to see it.  (See  discussion
          of new parameters below for definition of ACKWAIT.)

          Forcing  a channel access delay  for all stations  on the channel
          which  are  waiting for  a chance  to  transmit allows  ACKs from
          hidden  terminals to  get back  to the  expecting station.   This
          clears that traffic from the offered channel load.  If the packet
          was  indeed  copied  and  ACKed,  further  retrys  of   the  same
          information will not be necessary.











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          NEW PARAMETERS

          There  are several  new parameters  needed for  PriACK operation.
          See  the command description elsewhere in this document for their
          meanings and settings.

          1.  ACKPRIOR
          2.  DEADTIME 
          3.  ACKTIME
          4.  SLOTS
          5.  ACKWAIT (not directly user settable)

          This  timer actually consists of  the sum of  ACKTIME + DEADTIME.
          It  represents  the  time the  queued  up  TNC  will wait  before
          transmitting if it has selected the first slot.  This allows time
          for a hidden station's ACK to be sent on the channel.  

          It  is split  into  two  timers  because  it  has  two  unrelated
          components.  One is related  only to the data rate being  used on
          the channel (ACKTIME).  The other is related only to the absolute
          time the radios and TNC DCD circuits require to determine that  a
          transmitter is active after PTT is asserted (DEADTIME).

          OTHER RELATED PARAMETERS

          Several  of  the "standard"  TNC  parameters  will affect  PriACK
          operation.  Most of  these are parameters in TNCs  on the channel
          which are not using PriACK.























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          FRACK

          FRACK must be set correctly in any TNC regardless of protocol.

          FRACK should be set to  a value which allows time for  the TNC to
          send its packet  and receive the ACK.  This  value will depend on
          the settings being used for PACLEN  and the radio port data rate.
          This is because,  in many  TNCs, the  FRACK timer  starts at  the
          beginning of the packet rather than at the end!  Thus, it is best
          to set FRACK to its  worst case value for whatever data  rate you
          are using on the radio port and still allow for MAXFRAME 7 PACLEN
          255 packets to  be sent  and allow other  non-PriACK stations  to
          collide.  This  way you  can make adjustments  to PACLEN  without
          having to worry about interaction with the setting of FRACK.

          FRACK  should be set to 8 for 1200  baud work and 16 for 300 baud
          operation.

          RESPTIME

          If you are running PriACK on a channel where some of the stations
          have long RESPTIME  delays, those  stations will not  be able  to
          successfully communicate with  you after connecting.  If you wish
          to  communicate with  these stations  you will  have to  set your
          FRACK timer to a number  which is longer than the other  stations
          RESPTIME delay.

          RESPTIME  should be  set to  0 in  your TNC when  running PriACK.
          With proper DCD operation, RESPTIME 0 will work in any event.

          DWAIT

          DWAIT is  ignored when  running PriACK.  However, when  PRiACK is
          off, or  if you are  using a TNC  which does not yet  have PriACK
          capability, DWAIT should be set to DEADTIME, or 33 (330 mSec) for
          the default.

          TXDELAY

          TXDELAY should  be set  to allow  for the  slowest radio  oin the
          channel.   It  should be  the same  as DEADTIME  and DWAIT.   The
          default of 33 (330 mSec) is adequate for most work.









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          INITIAL PARAMETER SETTINGS SUMMARY

          The settings for use at 1200 baud on a VHF FM channel are:

          ACKPRIOR  ON
          SLOTS     3
          DEADTIME  33
          ACKTIME   14
          RESPTIME  0    (If you require a nonzero value for this parameter
                         in order to prevent ACKing individual packets in a
                         MAXFRAME greater than 1 blast, your DCD circuit is
                         not working.  Please get it fixed.) 
          DWAIT     33
          MAXFRAME    1-7 depending on channel quality
          FRACK     8

          The settings to use for 300 baud work on a linear mode HF channel
          are:

          ACKPRIOR  ON
          SLOTS     3
          DEADTIME  8
          ACKTIME   52
          DWAIT     8
          RESPTIME  0
          MAXFRAME    1 
          FRACK     16 
          PACLEN    32 to 128 depending on channel quality























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          Appendix C  Default Locations

          The default parameters for the various TNC 2 commands are located
          in the  1.1.8 EPROM.  The defaults  are documented here for those
          of  you who wish to change them for particular applications (such
          as  remotely  located  units,  etc.).   For  release  1.1.8,  the
          defaults table is found at address 0B98 hex.

          NOTE:   In future releases of firmware, this location may change.
          There is a pointer  at address 0055H which contains  the location
          of the default area in Z80 low-byte/high-byte format.

          WARNING!  The  TNC 2 firmware does not check  for valid defaults.
          If you  program  an  invalid default  (for  example,  parity  5),
          unpredictable results  may occur.   Be sure you  double-check any
          defaults you change!

          The defaults are listed in the table below.  All notes follow the
          table.

          EPROM               Value          Meaning   Command        Notes
          Address        (Hex)
          (Hex)
          0B98      21   33        DWAIT     33*10 mSec
          0B99      00   0         AXHANG    0*100 mSec
          0B9A      00   0         PACTIME   EVERY/AFTER* 
          0B9B      0A   10        PACTIME   10*100 mSec
          0B9C      21   33        DEADTIME  33*10 mSec
          0B9D      0E   14        ACKTIME   14*10 mSec
          0B9E      02   2         DLCTICKTIME    (do not change this)
          0B9F      01   1         CMDTIME   1*1 Sec
          0BA0      21   33        TXDELAY   33*10 mSec
          0BA1      05   5         reserved - must be 5
          0BA2      1E   30        TXTMOTMR  30*1 Sec       Note 1
          0BA3      01   1         TODVAL    1*1 Sec        Note 2
          0BA4      39   57        IDVAL     57*10 Sec      Note 3
          0BA5      00   0         RESPTIME  0*100 mSec     Stream A
          0BA6      00   0         RESPTIME  0*100 mSec     Stream B
          0BA7      00   0         RESPTIME  0*100 mSec     Stream C
          0BA8      00   0         RESPTIME  0*100 mSec     Stream D
          0BA9      00   0         RESPTIME  0*100 mSec     Stream E
          0BAA      00   0         RESPTIME  0*100 mSec     Stream F
          0BAB      00   0         RESPTIME  0*100 mSec     Stream G
          0BAC      00   0         RESPTIME  0*100 mSec     Stream H
          0BAD      00   0         RESPTIME  0*100 mSec     Stream I
          0BAE      00   0         RESPTIME  0*100 mSec     Stream J
          0BAF      0C   12        CHECK     12*10 Sec      Stream A
          0BB0      0C   12        CHECK     12*10 Sec      Stream B
          0BB1      0C   12        CHECK     12*10 Sec      Stream C
          0BB2      0C   12        CHECK     12*10 Sec      Stream D

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          EPROM               Value          Meaning   Command        Notes
          Address        (Hex)
          (Hex)
          0BB3      0C   12        CHECK     12*10 Sec      Stream E
          0BB4      0C   12        CHECK     12*10 Sec      Stream F
          0BB5      0C   12        CHECK     12*10 Sec      Stream G
          0BB6      0C   12        CHECK     12*10 Sec      Stream H
          0BB7      0C   12        CHECK     12*10 Sec      Stream I
          0BB8      0C   12        CHECK     12*10 Sec      Stream J
          0BB9      05   5         reserved - must be 5
          0BBA      00   0         reserved - must be 0
          0BBB      00   0         reserved - must be 0
          0BBC      00   0         reserved - must be 0
          0BBD      00   0         reserved - must be 0
          0BBE      00   0         reserved - must be 0
          0BBF      00   0         reserved - must be 0
          0BC0      00   0         reserved - must be 0
          0BC1      00   0         reserved - must be 0
          0BC2      00   0         reserved - must be 0
          0BC3      00   0         reserved - must be 0
          0BC4      01   1         BEACON EVERY/AFTER*,DEF EVERY
          0BC5      00   0         BEACON TIME (0 = never)
          0BC6      9C   'N'       MYCALL                   Note 4
          0BC7      9E   'O'
          0BC8      86   'C'
          0BC9      82   'A'
          0BCA      98   'L'
          0BCB      98   'L'
          0BCC      60   SSID 0
          0BCD      00   0         must be 0 - end of callsign string
          0BCE      40   ' '       MYALIAS                  Note 4
          0BCF      40   ' '
          0BD0      40   ' '
          0BD1      40   ' '
          0BD2      40   ' '
          0BD3      40   ' '
          0BD4      60   SSID 0
          0BD5      00   0         must be 0 - end of callsign string
          0BD6      08   8         FRACK     8*1 Sec
          0BD7      80   128       PACLEN
          0BD8      0A   10        RETRY
          0BD9      00   0         reserved - must be 0
          0BDA      04   4         MAXFRAME
          0BDB      07   7         AWLEN - must be 7 or 8
          0BDC      03   3         PARITY    EVEN           Note 5
          0BDD      00   0         AXDELAY
          0BDE      02   2         TXDELAYC
          0BDF      03   3         SLOTS
          0BE0      7C   '|'       STREAMSW Character
          0BE1      01   1         USERS

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          EPROM               Value          Meaning   Command        Notes
          Address        (Hex)
          (Hex)
          0BE2      0D   ^M        SENDPAC Character
          0BE3      18   ^X        CANLINE Character
          0BE4      19   ^Y        CANPAC Character
          0BE5      03   ^C        COMMAND Character
          0BE6      08   ^H        DELETE Character
          0BE7      16   ^V        PASS Character
          0BE8      12   ^R        REDISPLAY Character
          0BE9      13   ^S        STOP Character
          0BEA      11   ^Q        START Character
          0BEB      13   ^S        XOFF Character
          0BEC      11   ^Q        XON Character
          0BED      00   0         NULLS
          0BEE      00   0         SCREENLN
          0BEF      0000 0         CLKADJ
          0BF1      00   0         TAPRLATCH
          0BF2      00   0         MFILTER 1st Parameter
          0BF3      00   0         MFILTER 2nd Parameter
          0BF4      00   0         MFILTER 3rd Parameter
          0BF5      00   0         MFILTER 4th Parameter
          0BF6      00   0         MFILTER 5th Parameter
          0BF7      09   CMDS3                              Note 7
          0BF8      6A   CMDS4                              Note 8
          0BF9      44   CMDS5                              Note 9
          0BFA      00   CMDS6                              Note 10
          0BFB      20   CMDS7                              Note 11
          0BFC      3D   CMDS8                              Note 12
          0BFD      02   CMDS9                              Note 13
          0BFE      46   CMDS10                             Note 14
          0BFF      1F   CMDS11                             Note 15
          0C00      60   CMDS12                             Note 16
          0C01      B8   CMDS13                             Note 17
          0C02      60   CMDS14                             Note 18
          0C03      00   0         MYDLCNUM
          0C04      FE   254       DEFLTDLC
          0C05      00   0         Last Beacon Time - default to 0
          0C06      8D             reserved - must be 08DH
          0C07      00   0         reserved - must be 0
          0C08      00   0         reserved - must be 0
          0C09      00   0         reserved - must be 0
          0C0A      00   0         reserved - must be 0
          0C0B      00   0         reserved - must be 0
          0C0C      00   0         reserved - must be 0
          0C0D      00   0         reserved - must be 0
          0C0E      00   0         reserved - must be 0
          0C0F      00   0         reserved - must be 0
          0C10      00   0         reserved - must be 0
          0C11      00   0         reserved - must be 0

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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          EPROM               Value          Meaning   Command        Notes
          Address        (Hex)
          (Hex)
          0C12      00   0         reserved - must be 0
          0C13      00   0         reserved - must be 0
          0C14      00   0         reserved - must be 0
          0C15      00   0         reserved - must be 0
          0C16      00   0         reserved - must be 0
          0C17      00   0         reserved - must be 0
          0C18      86   'C'       UNPROTO CALL             See Note 4
          0C19      A2   'Q'
          0C1A      40   ' '
          0C1B      40   ' '
          0C1C      40   ' '
          0C1D      40   ' '
          0C1E      60   SSID 0
          0C1F      00   0         must be 0 - end of callsign string
          0C25           MFLAGS                             Note 19
          0C26           DFLAGS                             Note 20
          0C27           CONFLAG                            Note 21
          0C28           ENTRYSTA                           Note 22
          0C29           ENT2                               Note 23

          NOTES

          Note 1
               This is the timer which, when it is exceeded, increments the
               TXTIMEOUT Health counter.

          Note 2
               TODVAL  specifies the  number of  "ticks" the  DAYTIME clock
               increments each second.  It should always be set to 1.

          Note 3
               IDVAL is not otherwise settable.  It specifies the number of
               10-second intervals which elapse between IDs when HID is ON.

          Note 4
               Callsigns are  encoded per the  AX.25 standard document.   A
               callsign consists  of  six (6)  numbers  and letters.    The
               letters must be upper case and, if the callsign is less than
               six  (6) elements  long, must  be right-filled  with blanks.
               The ASCII  values corresponding  to the letters  and numbers
               must be left-shifted one bit.







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          Tucson Amateur Packet Radio                   TNC 2 System Manual

               The letters and numbers in HEX are:

          Char   ASCII Call                  Char   ASCII Call
        (BLANK)  20    40                    S      53    A6
          A      41    82                    T      54    A8
          B      42    84                    U      55    AA
          C      43    86                    V      56    AC
          D      44    88                    W      57    AE
          E      45    8A                    X      58    B0
          F      46    8C                    Y      59    B2
          G      47    8E                    Z      5A    B4
          H      48    90                    0      30    60
          I      49    92                    1      31    62
          J      4A    94                    2      32    64
          K      4B    96                    3      33    66
          L      4C    98                    4      34    68
          M      4D    9A                    5      35    6A
          N      4E    9C                    6      36    6C
          O      4F    9E                    7      37    6E
          P      50    A0                    8      38    70
          Q      51    A2                    9      39    72
          R      52    A4   


          A seventh  callsign  value is  the secondary  station ID  (SSID).
          This is a value from 0 through 15 and is encoded as:

          Bit  7    6    5    4    3    2    1    0
               0    1    1    D    C    B    A    0

          where D is the most significant bit and A the least in the binary
          value (0 through 15).

          Note 5

          Parity for the asynchronous serial port is:

               Value     Meaning 
                 0       None
                 1       Odd
                 2       None
                 3       Even









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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Note 6

          Binary status and  parameter elements  (commands whose  arguments
          are ON/OFF) are encoded as 

               ON  = TRUE  = 1
               OFF = FALSE = 0

          Commands which are "negative-true logic" (FALSE = 1 and TRUE = 0)
          are indicated by trailing asterisks (*).
          There  are  several defaults  that are  encoded  on a  bit basis.
          These are listed below.

          Note 7    CMDS3
               Bit  Command   Default
               7-   CMSG on/off
               6-   CONMODE   trans/conv*
               5-   NULF      on/off
               4-   NUCR on/off
               3-   LCOK      on/off
               2-   PASSALL   on/off
               1-   TXFLOW    on/off
               0-   AX25L2V2  on/off

          Note 8    CMDS4
               Bit  Command   Default
               7-   ESCAPE    on/off
               6-   XMITOK    on/off
               5-   DIGIPEAT  on/off
               4-   LFADD     on/off
               3-   BKONDEL   on/off
               2-   DELETE    on/off
               1-   ECHO on/off
               0-   BUDLIST   on/off

          Note 9    CMDS5
               Bit  Command   Default
               7-   CONSTAMP  on/off
               6-   DAYUSA    on/off
               5-   NEWMODE   on/off
               4-   reserved
               3-   MCOM on/off
               2-   MALL on/off
               1-   HID       on/off
               0-   HEADRLN   on/off






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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Note 10   CMDS6
               Bit  Command   Default
               7-   STREAMCA  on/off
               6-   STREAMDB  on/off
               5-   reserved
               4-   reserved
               3-   reserved
               2-   8BITCONV  on/off
               1-   TRFLOW    on/off
               0-   MSTAMP    on/off

          Note 11   CMDS7
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   LCSTREAM  on/off
               4-   reserved
               3-   NOMODE    on/off
               2-   RXBLOCK   on/off
               1-   HEALLED   on/off
               0-   CBELL     on/off

          Note 12   CMDS8
               Bit  Command   Default
               7-   LFIGNORE  on/off
               6-   CMSGDISC  on/off
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   reserved
               0-   reserved

          Note 13   CMDS9
               Bit  Command   Default
               7-   reserved
               6-   BBSMSGS   on/off
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   reserved
               0-   reserved








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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Note 14   CMDS10
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   reserved
               0-   reserved

          Note 15   CMDS11
               Bit  Command   Default
               7-   reserved
               6-   MNONAX25  on/off
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   TXUIFRAM  on/off
               0-   FIRMRNR   on/off

          Note 16   CMDS12
               Bit  Command   Default
               7-   reserved
               6-   ACKPRIOR  on/off
               5-   TXDIDDLE  on/off
               4-   KISS      on/off
               3-   CHECKV1   on/off
               2-   reserved
               1-   reserved
               0-   reserved

          Note 17   CMDS13
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   reserved
               2-   BLP       on/off
               1-   reserved
               0-   reserved








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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Note 18   CMDS14
               Bit  Command   Default
               7-   reserved
               6-   ANSWRQRA  on/off
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   reserved
               0-   reserved

          Note 19   MFLAGS
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   TRACE     Off
               2-   MCON On
               1-   MRPT On
               0-   MONITOR   On

          Note 20   DFLAGS
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   reserved
               0-   reserved

          Note 21   CONFLAG
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   FLOW On
               3-   CR        On
               2-   reserved
               1-   FULLDUP   Off
               0-   CONOK     On








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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Note 22   ENTRYSTA
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   reserved
               2-   reserved
               1-   AUTOLF    On
               0-   reserved

          Note 23   ENT2
               Bit  Command   Default
               7-   reserved
               6-   reserved
               5-   reserved
               4-   reserved
               3-   reserved
               2-   XFLOW     On
               1-   reserved
               0-   reserved






























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          Tucson Amateur Packet Radio                   TNC 2 System Manual

          BIBLIOGRAPHY




          American Radio Relay League, The 1985 ARRL Handbook for the Radio
          Amateur, 1984, pp. 19-21 through 19-31.

          American  Radio  Relay  League,  Proceedings of  the  First  ARRL
          Amateur  Radio  Computer  Networking  Conference,  October 16-17,
          1981.

          American  Radio  Relay League,  Proceedings  of  the Second  ARRL
          Amateur Radio Computer Networking Conference, March 19, 1983.

          American  Radio  Relay  League,  Proceedings of  the  Third  ARRL
          Amateur Radio Computer Networking Conference, April 15, 1984.

          American  Radio  Relay League,  Proceedings  of  the Fourth  ARRL
          Amateur Radio Computer Networking Conference, March 30, 1985.

          American  Radio  Relay  League,  Proceedings of  the  Fifth  ARRL
          Amateur Radio Computer Networking Conference, March 9, 1986.

          American  Radio  Relay  League,  Proceedings of  the  Sixth  ARRL
          Amateur Radio Computer Networking Conference, August 29, 1987.

          American  Radio Relay  League,  Proceedings of  the Seventh  ARRL
          Amateur Radio Computer Networking Conference, October 1, 1988.

          American  Radio  Relay League,  Proceedings  of  the Eighth  ARRL
          Amateur Radio Computer Networking Conference, October 7, 1989.

          American Radio  Relay League, Proceedings of  the Ninth ARRL/CRRL
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          American Telephone  and  Telegraph Company,  "Operations  Systems
          Network  Communications Protocol  Specification BX.25,"  Issue 2,
          Publication 54001, 1979.

          David W. Borden, K8MMO, and Paul L. Rinaldo, W4RI, "The Making of
          an Amateur Packet-Radio Network," QST, October 1981, pp. 28-30.

          D. W. Davies, D. L. A. Barber, W. L. Price and C. M. Solomonides,
          Computer Networks and Their Protocols, John Wiley and Sons, 1979.

          Exar Integrated  Systems,  "Phase-Locked Loop  Data  Book,"  Exar
          Applications Note  AN-01, P. O.  Box 62229, Sunnyvale,  CA 94088,
          1981.


                                         197








          Tucson Amateur Packet Radio                   TNC 2 System Manual

          Terry   Fox,  WB4JFI,  "AX.25   Amateur  Packet-Radio  Link-Layer
          Protocol, Version 2.0," ARRL,  October, 1984 (Available from ARRL
          for $8).

          International  Standards Organization,  "Reference Model  of Open
          Systems Architecture," Document ISO/TC97/SC16/N227, June 1979.

          Lyle  Johnson, WA7GXD,  "Join  the  Packet-Radio Revolution,"  73
          Magazine, September, 1983, pp. 19-24.

          Lyle Johnson,  WA7GXD, "Join  the Packet-Radio Revolution  - Part
          II," 73 Magazine, October, 1983, pp. 20-31.

          Lyle Johnson,  WA7GXD, "Join  the Packet-Radio Revolution  - Part
          III," 73 Magazine, January, 1984, pp. 36-44.

          Margaret Morrison,  KV7D, and Dan Morrison,  KV7B, "Designing the
          TAPR TNC  Audio Input  Filter," Proceedings  of  the Second  ARRL
          Amateur Radio Computer Networking  Conference, March 19, 1983, p.
          54.

          Margaret Morrison, KV7D, and  Dan Morrison, KV7B, "Amateur Packet
          Radio: part 1," Ham Radio, July 1983, pp. 14-25.

          Margaret Morrison,  KV7D, Dan  Morrison, KV7B, and  Lyle Johnson,
          WA7GXD, "Amateur  Packet Radio: part 2," Ham  Radio, August 1983,
          pp. 18-28.

          National  Semiconductor,  "Technical Product  Information, MF10",
          2900 Semiconductor Drive, Santa Clara, CA 95051.

          Harold E.  Price, NK6K, "Multi-use Design  Considerations for the
          TAPR TNC," Proceedings of the  Second ARRL Amateur Radio Computer
          Networking Conference, March 19, 1983, p. 62.

          Harold Price, NK6K, "What's  All This Racket About Packet?"  QST,
          July, 1985, pp. 14-17.

          Harold Price, NK6K, "A Closer Look at Packet Radio," QST, August,
          1985, pp. 17-20.

          Andrew S. Tanenbaum, Computer Networks, Prentice-Hall, 1981.









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