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XRPi Documentation - Interfacing

TTY Interface

A TTY ("TeleTYpe") interface allows the sysop to use a "dumb terminal" or equivalent "terminal emulator" (e.g. Procomm / Telix on DOS or Hyperterm on Windows) to access XRPi via an RS232 serial connection. The interaction is via plain ASCII text. 


		.------.         .----------.
		|      |         |   Dumb   |
		| XRPi |----<----| Terminal |
		|      |  RS232  |(HW or SW)|
		'------'         '----------'

This would typically be used where the machine running XRPi either did not have a monitor, or was located somewhere remote from the operating position, e.g. in an outbuilding.

TTY provides a simple solution in cases where the machine running XRPi has a spare RS232 port but does not have a LAN adaptor or Ethernet connection, e.g. an old low-spec laptop.

The Raspberry Pi has a LAN adaptor of course, but maybe you don't want to risk leaving it connected to your network? TTY to the rescue!

The COM ports on the two machines may be interconnected by a simple 3-wire (TXD, RXD and Ground) "NULL-Modem" RS232 cable.

Configuration

A TTY connection 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=ASCII. Choose SPEED to suit the peripherals, and MTU=256. For example: 

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

Flow control is optional, and if not specified, it defaults to NONE. Be VERY careful if you are tracing over a flow controlled link, because if you pause the display for a long time, the data will back-up in XRPi, and may eventually halt the program.

Operation

Operation from a dumb terminal is very much the same as operating via a modem or packet link. Everything is plain text, and you can send commands and receive responses, make connections etc. But you cannot view the XRPi display.

Notes

The use of "TTY" (upper case) dates right back to DOS XRouter, and has been carried forward via XR32 to XRPi. But as Linux also has a "tty" (lower case) interface, this could possibly cause some confusion.

See Also