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 iv 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 v 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 1 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 . The 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 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 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 . 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 20 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 () whenever it displays a carriage return (). Set AUTOLF OFF to keep the TNC from also adding an . 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 (or 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 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 ), or NULF ON (delay after ). 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 21 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 . Hello, there. Hello, there. The 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 ), 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 22 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 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 . The TNC doesn't echo the , but you should immediately see a Command Mode prompt. To return to Converse Mode, enter the command CONVERS: cmd:CONVERS Whatever I type in Converse Mode is transmitted. Whatever I type in Converse Mode is transmitted. 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. 23 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 24 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 25 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. 26 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. 27 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 , 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: 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 28 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 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 . (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 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 character. You can change this character with the command DELETE. If you set DELETE ON, you can erase characters by typing the character; setting DELETE 29 Tucson Amateur Packet Radio TNC 2 System Manual OFF returns to using . You will probably want to use the same key that your computer normally uses to rub out characters. is more commonly used than by personal computers. If you aren't sure whether your rubout key produces or 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 (). 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 . The TNC will display a followed by . If you are in Command Mode, you will see a new prompt: cmd:Hi, John, how are you?\ [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 : cmd:CONNECT KB7\\\WA7\ [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 . To resume output from the TNC to your computer, 30 Tucson Amateur Packet Radio TNC 2 System Manual enter . 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 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, . For example, I wasn't at the meeting. What happened? Ordinarily, this message would be sent as two packets. By prefixing the first with , the operator sends it all at once, but maintains the 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 2) Manually send an unconnected packet cmd: CONVERSE ^C cmd: 31 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: 32 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 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 33 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 NUL 16 $10 DLE 1 $01 SOH 17 $11 DC1 2 $02 STX 18 $12 DC2 3 $03 ETX 19 $13 DC3 4 $04 EOT 20 $14 DC4 5 $05 ENQ 21 $15 NAK 6 $06 ACK 22 $16 SYN 7 $07 BEL 23 $17 ETB 8 $08 BS 24 $18 CAN 9 $09 HT 25 $19 EM 10 $0A LF 26 $1A SUB 11 $0B VT 27 $1B ESC 12 $0C FF 28 $1C FS 13 $0D CR 29 $1D GS 14 $0E SO 30 $1E RS 15 $0F SI 31 $1F US 127 $7F 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. 34 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 after in data sent to terminal 35 Tucson Amateur Packet Radio TNC 2 System Manual BKONDEL Echo after character deletion ECHO Automatic echo of serial port input FLOW Type-in flow control LCOK Lower case translation NUCR Nulls after NULF Nulls after NULLS Null count SCREENLN Automatic 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 . 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: 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. 36 Tucson Amateur Packet Radio TNC 2 System Manual 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 , 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 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 , 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. 37 Tucson Amateur Packet Radio TNC 2 System Manual 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 after BKONDEL Echo after character deletion ECHO Automatic echo of serial input ESCAPE translation FLOW Type-in flow control LCOK Lower case translation NUCR Null characters after NULF Null characters after NULLS Null count SCREENLN Automatic 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. 38 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 ) 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. 39 Tucson Amateur Packet Radio TNC 2 System Manual 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 ) to request that the output stop and another special character (usually ) 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 and 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, 40 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 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. 41 Tucson Amateur Packet Radio TNC 2 System Manual 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 42 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: 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 *** 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 s by prefixing them with the pass character: cmd:CTEXT Sorry, I can't talk right now. I'll be on the air again after 8 PM. 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 43 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 , you probably want the 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 after each 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. 44 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 f