[plug] Easymail
Denis Brown
dsbrown at cyllene.uwa.edu.au
Fri Mar 19 14:26:32 WST 1999
Mike Holland wrote in part...
>Anyway, reverse engineering the protocol sounds like fun.
>Is there any existing software to log two rs-232 streams in parallel, so
>you can see the sequence afterwards?
>
Too much of a newbie to know about such software on Linux but here's an
old-timer's trick which worked reliably bL (before Linux).
Take two silicon signal diodes (1N914, 1N4148 or similar) and connect their
anodes together (un-banded ends). To this common anode connection, add one
end of a 10 kilohm resistor. That forms the "output" signal which you wire
to the Rx line of your snooper port. Then take one cathode (banded end) to
each of pins 2 and 3 on the RS232 connector carrying the data stream. The
unused end of the resistor goes to a 9 to 12-ish volt positive supply
(positive wrt ground); a 9-volt transistor radio battery works well. In
some cases the resistor and positive supply isn't needed -- just depends on
how critical your snooper Rx interface chip is about otherwise floating Rx
lines :-) There's no magic in teh choice of 10 kilohm, either; anything
from 7.5 kilohm through to 33 kilohm should work okay, it's just a bleed
after all.
As long as the snooper is able to swallow incoming data without dropping
bits, you'll capture both streams. That technique was a Godsend in earlier
days. No reason for it not to work just as well now. Yes, you'll probably
have to eyeball at least some of the data stream but with any luck the eol
character(s) will be obvious so the streams should be easy to seperate.
HTH
Cheers,
Denis
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