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From: nigelh@uvicctr.UUCP (Nigel Horspool)
Newsgroups: net.micro.pc
Subject: Re: Running IBM serial boards at 19.2KB
Message-ID: <120@uvicctr.UUCP>
Date: Sun, 21-Apr-85 15:45:36 EST
Article-I.D.: uvicctr.120
Posted: Sun Apr 21 15:45:36 1985
Date-Received: Tue, 23-Apr-85 06:25:13 EST
References: <145@cernvax.UUCP> <138@omen.UUCP> <535@cyb-eng.UUCP>
Distribution: net.micro.pc
Organization: University of Victoria, Victoria B.C. Canada
Lines: 27

> > The standard IBM serial adapter using the 8250 UART, as well as the
> > serial ports on expansion boards such as AST SIXPACK can be programmed
> > for 19200 and 38400 bits per second.
> 
> Huh?  I quote from page 1-238 of the I.B.M. PC2 Technical Reference manual:
> 
> 	Note:  The maximum operating frequency of the baud generator is
> 	3.1MHz.  In no case should the data rate be greater than 9600 baud.
> 
> Do you know something IBM doesn't?
> 

	I have coded my own VT100 terminal emulator program to run under
Coherent Unix on the PC/XT.  My program uses its own assembler-coded 
interrupt routines to handle I/O and, despite what the IBM manual says,
it operates perfectly at 19200 baud.  Possibly the emulator will work
at 38.4Kb too, but I don't have any equipment at home to test this
speed.  According to some (rough) calculations, the XT will have time to
execute about 300 instructions between two interrupts when serving
interrupts produced by a 38.4Kb I/O device.  A carefully coded interrupt
routine should easily be able to keep up without missing any interrupts.

			R. Nigel Horspool
			University of Victoria

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