Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!ncar!gatech!udel!rochester!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.os.minix
Subject: Serial port speeds (was Re: AN HISTORIC MOMENT!)
Summary: sure you can go faster than 9600
Message-ID: <22de01d6@ralf>
Date: 15 Jul 88 13:00:06 GMT
Sender: netnews@pt.cs.cmu.edu
Lines: 20
In-Reply-To: <4200004@hpihoah.HP.COM>

In article <4200004@hpihoah.HP.COM>, bruce@hpihoah.HP.COM (Bruce LaVigne) writes:
}actually stuff into the chip are divisors of an externally input clock.  With
}the clock that IBM used, if you go above 9600 you start using non-integer
}divisors.  What this means is that since you can really only use integer
}numbers into the chip as a divisor, you don't get 19200 but something kindof
}close.  If the other side can handle it, fine, but IBM doesn't support it.

That is not correct.  The divisor for 9600 is 12, so the divisor for 19200 is
6 and for 38400 it is 3.  As a matter of fact, it is the 110 baud that is
off by a small fraction of a percent, whereas 300/600/1200/2400/etc are all
exact (assuming that the clock is exact).

However, from what I have heard, early 8250's had problems sync'ing with the
incoming signal at >19200.  I believe that the various 115k transfer
programs use two stop bits to help the chip recognize the incoming data.

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