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From: davidsen@steinmetz.steinmetz.UUCP (William E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Looking for 115k Baud, honest!
Message-ID: <7780@steinmetz.steinmetz.UUCP>
Date: Thu, 5-Nov-87 14:49:38 EST
Article-I.D.: steinmet.7780
Posted: Thu Nov  5 14:49:38 1987
Date-Received: Sun, 8-Nov-87 03:47:52 EST
References: <4594@spool.wisc.edu>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Distribution: comp
Organization: General Electric CRD, Schenectady, NY
Lines: 30
Keywords: 115k Baud, Serious Serial Port, Help!, serious hacking

In article <4594@spool.wisc.edu> jojo@speedy.WISC.EDU (Jon Wesener) writes:
|
|	Believe it or not, I need to make my serial port go 115K Baud!
|I saw code to do this once, but I'm not sure where,  If anyone has
|any ideas, examples, CODE! which does this, please send me mail!!!!

In the 8250 there are two divisor fields. On is a two bit field
controlling divide clock by 64, 16, 1, or syncronous operation. There is
also a 16bit counter quantity which is used to dicide down the clock
(which has already been divided by 1,16, or 64).

How to use it.

The clock rate is 115200, so if you set the count to 1, you will operate
at 115200 bps. There is no guarantee that this will work, since the chip
is rated at most for 19200, but that's the way it's done. You may have
to upgrade your 8250 with another (compatible) chip, I don't have the
number handy, but I seem to recall Signetics and/or AMD (please help me
some hardware guru).

Note that all of the common baud rats are factors of 115200. The only
two which don't come out exactly are 110 and 134.5, which are close
enough to work in most cases anyway.

I would have mailed this, but I think it may be of general interest. The
details start on page 6 of the AT tech ref, volume 2.
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs | seismo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me