[ILUG] Reverse engineering serial protocol

[Dale Dunlea]

Hi All,

I need to puzzle out an RS232 serial protocol. I made a rather silly
presumption and bought a touch screen (CTX PV500T) and assumed that it
wouldn't need any fancy drivers but would just work as a standard serial
mouse.

This of course was wrong seeing as how a mouse reports relative
coordinates while a touch screen works on absolute coordinates. But I
reckon it should be a reasonably straight forward matter to puzzle out
what it's doing.

The first thing I need to do is verify the baud rate. I suspect that it
is 9600 8N1, but have no way of being sure. Does anyone know of a way to
verify the baud-rate/data/parity/stop-bits for an RS232 interface that
doesn't require an oscilloscope?

I've tried listening with minicom, and wrote a program to read bytes
from /dev/ttyS0 and print them to the screen in the hope of something
readily apparent, but no joy so far. My next step is to connect an RS232
cable from my linux box to my windows laptop that has the drivers
installed, sned it some characters, and see what the mouse pointer does.

I've googled and only found drivers for other manufacturers. Don't
suppose anyone else has had any experience with such a device? 

Thanks in advance,
Dale.

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