Date   : Sun, 22 Jul 2012 13:30:31 +0100
From   : walker_matt@... (Matthew Walker)
Subject: RS423 won't transmit. Dead 6850?

After trying the longer program, with the loopback in place the sending
out line displays correctly, coming in stays empty, keyboard and serial
input buffers stay empty and the serial out buffer stays at 191.
If the RTS - CTS wire is disconnected the serial output buffer will
count down until it reaches 0 (typing quickly fills the keyboard
buffer), once the serial out buffer fills up the keyboard buffers starts
to fill. Once the RTS - CTS wire is reconnected the serial output buffer
will then return to 191 and the input buffer stays empty. From this i'm
guessing RTS and CTS work, and seeing as I can receive data  from a PC,
RxD must work.