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XRPi Documentation - Interfacing

TNC2 Emulator

The TNC2 Emulator is a feature which allows RS232 devices such as weather stations, dumb terminals, GPS and telemetry devices to send and receive packets as if they were connected to a real TNC2. 


		\|/            .------.
		 |   .-----.   |      |         .-----.
		 '---| Rig |---| XRPi |----<----| GPS |
		     '-----'   |      |  RS232  '-----'
		               '------'

For example, imagine you have a weather station which is designed to be connected to a TNC via an RS232 cable. Now imagine that you already have an APRS port on your XRPi. How would you get your weather station on air?

You could use an additional TNC, radio and antenna, but that would be a pointless duplication of equipment. Far better to set up XRPi to emulate a TNC so that it can interface directly to the weather station, allowing the weather station to send to, and receive from, the existing APRS port.

Or you may have a dumb terminal connected to XRPi via an RS232 cable, and use it to monitor any port, make connections with other stations etc. This is completely independent of XRPi's command interface, and does not require a session with the node.

There are several applications which have TNC2 as one of the interface options. You may interface them to any of XRPi's radio ports via that means.

Or perhaps you wish to monitor a radio channel with a data logging program, or send the channel activity to a serial printer? The possibilities are limited by your imagination.

Configuration

The emulator requires only an INTERFACE in XROUTER.CFG. It does *not* require a PORT. It is configured by defining an INTERFACE with TYPE=ASYNC and PROTOCOL=TNC2. Choose SPEED to suit the peripherals, and MTU=256. For example: 

           INTERFACE=5
                TYPE=ASYNC
                COM=/dev/ttyUSB1
                SPEED=19200
                PROTOCOL=TNC2
                MTU=256
           ENDINTERFACE

You can have as many TNC emulators as you wish, providing you have an RS232 port for each one. You should preferably use a different MYCALL or SSID for each one if there is any chance of more than one TNC being used on the same radio port.

Operation

Standard TNC2 commands currently recognised are Ctrl-C, AUTOLF, CONNECT, CONVERSE, DISCONNECT, ECHO, FLOW, K, MCON, MONITOR, MYCALL, PORT, and UNPROTO. Others may be implemented upon request.

You may set the TNC's callsign (using MYCALL) completely independently of XRPi's callsign, and may select any of XRPi's radio ports using the PORT command. When you select a port, the TNC2 emulator receives from, and transmits to, the radio equipment connected to that port.

All settings are saved to the file TNCn.CFG where 'n' is the interface number. This file is automatically created if it doesn't already exist. It is read when XRPi starts up, so the TNC always returns to its previous configuration. The file contains binary data, so you must not attempt to edit it.

Note: The emulator does not currently accept incoming connections. That facilitity may be added upon request.

See Also