Path: utzoo!mnetor!tmsoft!torsqnt!hybrid!scifi!bywater!uunet!paralogics!shaw
From: shaw@paralogics.UUCP (Guy Shaw)
Newsgroups: comp.dcom.modems
Subject: What is special about "AT" (was Re: Hayes Microcomputer lawsuit???)
Message-ID: <424@paralogics.UUCP>
Date: 3 Feb 91 23:34:42 GMT
References: <143271@pyramid.pyramid.com> <3763.27aaed7c@hayes.uucp>
Organization: Paralogics
Lines: 36

In article <3763.27aaed7c@hayes.uucp> tnixon@hayes.uucp writes:

> [. . .]                     But even the specifics related to 
>detecting the speed and format from the "AT" predated Hayes' first 
>Smartmodem. [. . .]

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.

I suppose that the completely naive approach is to keep cycling through
settings until you see a proper 'A'.  But then it would not matter what
prefix was chosen, as long it is agreed upon in advance.  But, if I
understand correctly, some characters are better than others because
they produce a greater number of distinct results for all combinations
of sending and listening settings, and this information can be used to
quickly narrow down the number of possible settings to try when listening
for the next character.

Why did tips on the Arpanet use "@"?
Why did Hayes (or whoever it might have been before them) choose "AT"?

Is there any literature on this subject?  Or, is this really just one
of those black arts that gets passed down informally from mentor to
acolyte, or, even worse, gets inherited in the form of code and tables
in ancient source code that works but no one dares tamper with?
If the answer is RTFM, please do tell me which FM.  I have a few books
on communications, but this does not seem to be one of the hot topics.
I have not seen it discussed in this newsgroup, but then, I have been
reading this newsgroup for only about a year.
--
Guy Shaw
Paralogics
paralogics!shaw@uunet.uu.net  or  uunet!paralogics!shaw