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From: marc@aria.ascend.com (Marco S Hyman)
Newsgroups: comp.dcom.modems
Subject: Re: What is special about "AT"
Message-ID: <401@aria.ascend.com>
Date: 4 Feb 91 17:55:16 GMT
References: <143271@pyramid.pyramid.com> <3763.27aaed7c@hayes.uucp>
	<424@paralogics.UUCP>
Organization: Ascend Communications -- San Francisco
Lines: 19

In article <424@paralogics.UUCP> shaw@paralogics.UUCP (Guy Shaw) writes:
    I am curious - is there some property of the prefix "AT" that makes it
    more suitable for the automatic detection of settings than other prefixes?
    By settings, I mean such things as speed, parity, character size,
    start/stop bits, etc.

There are many pairs that are as good as AT.  What you are looking for is a
character pair where each character has different parity and the first bit
transmitted of the first character (the low order bit of the "A") is a one
bit.  This allows the receiver to autobaud by measuring the length of the
start bit (a zero bit) and determine parity (odd, even, mark, or space) by
comparing the high order bit of the two characters.

Why AT? Maybe Toby knows.  (ATtention, ATlanta, ???)

// marc
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