[ILUG] Reverse engineering serial protocol

[Dale Dunlea]

> <snip>
> > 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.
> <snip>
> 
> I know you say you've tried minicom, but have you tried all 
> the baud rate/stop-start-bit combinations? By varying these 
> you should be able to find out the serial parameters that the 
> screen is using. 

I have tried a whole range of these, but minicom outputs data regardless
of which baud rate I use, so it's hard to know what the "right" setting
is seeing as how they all produce data.

> The screen won't necessarily be outputting 
> regular  ol' ASCII though. I don't know if minicom is cable 
> of displaying output in hex, but according to google GTKTerm 
> (a hyperterm clone) is. Cian

The program I wrote that reads from /dev/ttyS0 outputs as binary, hex,
and decimal. Binary seems to be offering me something approaching a clue
in that the last byte read is always equal to the second-last byte read,
but with bit 6 negated. This consistency is leading me to believe that I
may be on the right track, but so far, it is all guess-work.

Regards,
Dale.