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PICList Thread
'Odd RS232 problem.'
2000\02\24@091806 by andy howard

I have an odd problem with an F84 project I've just built.

The circuit is straightforward, it's just an F84 and 4MHz resonator,
output via a MAX202. Only TX and Ground are connected at the output.

The application is to decode one of 16 switches wired as a matrix and to
send a corresponding string via RS232 at 9600 to control a commercial
Keyboard Video and Monitor (KVM) switcher.

I've used the FED WizPIC library code for write the app, and it
simulates OK. When I connect the box to a PC running Terminal or
Hyperterminal it outputs all the correct character strings followed by
<CR> and <LF> as required. There is no flow control or handshaking used
or required. At this stage I'm happy that the software is well behaved.

When I connect a PC to the the switcher it controls it via Hyperterminal
using these selfsame codes.

You've probably guessed by now, when the PIC box is connected to the
switcher zilch occurs, whether connected via a straight cable or a tx/rx
reversed one.

This is driving me mad, everything works individually. Put it together
and, nothing.

Any suggestions would be very welcome. Please help to preserve my little
remaining untorn hair...



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           `-'                                               `-'


2000\02\24@095730 by Alan Pearce

face picon face
Are you sure you have hard wired the modem control signals correctly for
HyperTerminal to operate? Or set HyperTerminal to ignore control signals? this
is the usual gotcha for this type of problem.

2000\02\24@120909 by Andrew Kunz

On a PC, you usually have to tie the handshaking lines together to make it work,
even with 3-wire connections:

On a 9-pin connector, tie




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