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From: kaleb@mars.jpl.nasa.gov (Kaleb Keithley)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: How do get COMx to do 19,200 baud
Message-ID: <2956@jato.Jpl.Nasa.Gov>
Date: 1 Mar 90 18:32:31 GMT
References: <32894@prls.UUCP>
Sender: news@jato.Jpl.Nasa.Gov
Reply-To: kaleb@mars.UUCP (Kaleb Keithley)
Distribution: usa
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Lines: 27

In article <32894@prls.UUCP> gordon@prls.UUCP (Gordon Vickers) writes:
>   my initial study, it seems that my main problem will be trying to
>   get an RS232 serial port to communicate at 19,200 baud.  One solution
>
>       Any recommendations on how to do 19,200 baud on a serial port? One
>

PC serial ports have no problem in general running 19200, and even 38400 baud,
the problem lies in the BIOS, which (as a result of IBM's brain damaged lack
of foresight) does not have the logic to set the hardware to do 19200.  Five
years ago I coerced a 5mhz XT to run 19200 and 38400 by getting the BIOS
listing from the IBM Hardware Tech Ref, copying it into my own code, and
modifying it to set the correct divisor for the higher rates of speed.

The divisor starts out fairly large, for low baud rates, eventually getting
to 4, for 9600, 2 is the divisor for 19200, and 1 for 38400.  Like I said,
it was five years ago, so I don't have the code fragment around anymore, or I'd
send it to you.  You might also check on simtel20 or some place for similar
samples.

I think the XTs I used were right on the hairy edge of working, i.e. not being
able to keep up at 38400, but I'd *think* that an AT should have no problem.

Chewey, get us outta here!
                 
kaleb@mars.jpl.nasa.gov            Jet Propeller Labs
Kaleb Keithley