Date   : Wed, 18 Jul 2012 23:16:25 +0100
From   : jgh@... (J.G.Harston)
Subject: RS423 won=27t transmit=2E Dead 6850?

Matthew Walker wrote:
> I've a plain Issue 7, which can't transmit anything from the RS423 
> port.
...
> anyone have any ideas I could try before I have to de-solder the 
> 6850?

If you make a serial loopback plug with RTS connected to CTS and RxD
connected to TxD you can do a simple test to check the serial port is
physcially working. I used to carry such a plug around as a first 
simple
test. Use the following very very dumb terminal program:

10 REM > SerTest
20 ON ERROR OSCLI"FX3":OSCLI"FX2":REPORT:PRINT:END
30 *FX2,2
40 REPEAT
50  IF ADVAL(-1):OSCLI "FX3,1":VDU GET:OSCLI "FX3"
60  IF ADVAL(-2):OSCLI "FX2,1":VDU GET:OSCLI "FX2,2"
70 UNTIL FALSE

If the serial port works, then keypresses will be echoed to the VDU.

JGH