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From: david@csource.oz.au (david nugent)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: MIDI
Message-ID: <758@csource.oz.au>
Date: 17 Nov 90 16:16:09 GMT
References: <4840.tnews@basso.actrix.co.nz> <3341@bruce.cs.monash.OZ.AU> <1990Nov14.052315.988@vax5.cit.cornell.edu> <1502@cnps.PHILIPS.nl>
Distribution: comp
Organization: Unique Computing Pty Ltd, Melb, Aust.
Lines: 23

In <1502@cnps.PHILIPS.nl> dickw@cnps.PHILIPS.nl (Dick Wiersma) writes:

> I can't remember how the IBM serial port gets its UART clock 
> frequency but I do remember that most UART have some built-in 
> divider to obtain its internal clock frequency from a crystal 
> frequency. This divider (in most cases) is an ordinary 2^x divider.

The PC's baud rate divisor is - "strangely enough" - 115200.


> By choosing an appropriate crystal frequency they are able to let 
> the UART "talk" the standard Baud rates like 300, 600, 1200, 2400,
> 4800, 9600, 19200 and 38400.

There are two other possible baud rates between 19200 and 38400. These
are 23040 and 28800; and their corresponding divisors are 0005H and 0004H
respectively.

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