AT&T 3B1/Telebit modem compatibility problem

[Mark Dapoz]

In article <1990May23.183735.9239 at sonyd1.uucp> bruce at sonyd1.uucp (Bruce Lilly) writes:
>It seems that the built-in modem in the AT&T 3B1 (a.k.a. 7300) has some
>problems when communicating with Telebit modems at 1200 baud. The
>problem occurs when the OBM calls out to a Telebit which is set to
>provide the PEP answer tones first. The symptom is a sequence of
>correctly received characters (about 20) followed by gibberish.

This problem only occurs when talking to a telebit which has locked the
interface speed (ie. S51 = [0-5]).  I think the problem was that one of
the modems (the telebit I believe) is cutting the stop bits a little bit
short of what the other expects, and as a result you get garbage.  For some
reason the problem disappears when you get the telebit to autobaud the
interface.

>At this point, I suspect either a hardware problem, or a problem with the
>driver for the OBM (assuming it hasn't changed between 3.51 and 3.51m).

As you've found out, the OBM is very picky with what it's communicating with.
Do yourself a favour and pick up a cheap 2400 baud modem and hook it up to
the serial port.

>Has anybody else experienced this problem, and if so, are there any
>workarounds (short of using 300 baud, which does work) or bug fixes?

See above, I got it to work that way but I don't guaranatee that it'll still
work since I don't use the OBM and my telebit now has V5 roms.
-- 
Managing a software development team 	|   Mark Dapoz  
is a lot like being on the psychiatric	|   mdapoz%hybrid at cs.toronto.edu
ward.  -Mitch Kapor, San Jose Mercury	|   ...uunet!mnetor!hybrid!mdapoz