Path: utzoo!utgpu!attcan!uunet!seismo!esosun!ucsdhub!hp-sdd!ncr-sd!matt
From: matt@ncr-sd.SanDiego.NCR.COM (Matt Costello)
Newsgroups: comp.dcom.modems
Subject: Re: Autobaud Matching
Keywords: autobaud, usart
Message-ID: <2621@ncr-sd.SanDiego.NCR.COM>
Date: 21 Sep 88 03:16:32 GMT
References: <56.015163@adam.DG.COM> <9262@cup.portal.com>
Organization: NCR Corporation, Rancho Bernardo
Lines: 25

In article <9262@cup.portal.com> thad@cup.portal.com writes:
>In general, autobaud detection necessitates your system being set up at some
>"high" baud and analyzing the bits that arrive when a caller types some
>character (typically a carriage return).

It is easy if you've got a USART rather than a UART.  Place the USART
into synchronous mode with a clock rate several times higher than your
maximum expected baud rate.  You can then measure the bit times of
the first incoming character.  Take the smallest bit period and that
is your bps rate.  Under normal circumstances you will want to constrain
the bit rates to 'legal' values.

This sort of thing was real common back in the days of the Intel 8251,
and was the one thing I missed when the WD 8250 "ACE" replaced it as
the chip of choice.  With the 8251, putting it into synchronous mode gave
you the raw bit data at 16 times the bps rate.


At the system level the easiest autobauding consists of using a "smart"
modem that will convert everything on your side to a fixed rate.  It is
much easier to let the modem manufacturers worry about it.
-- 
Matt Costello	
+1 619 485 2926	
		{ucsd,att,pyramid,nosc.mil}!ncr-sd!matt