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From: hamilton@uxc.cso.uiuc.edu.UUCP
Newsgroups: comp.misc
Subject: Re: How do PCs talk 115kbps?
Message-ID: <177200004@uxc.cso.uiuc.edu>
Date: Sun, 7-Jun-87 16:16:00 EDT
Article-I.D.: uxc.177200004
Posted: Sun Jun  7 16:16:00 1987
Date-Received: Wed, 10-Jun-87 04:34:20 EDT
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Nf-From: uxc.cso.uiuc.edu!hamilton    Jun  7 15:16:00 1987


davidsen@steinmetz (bill davidsen) says:
> In article <1463@ho95e.ATT.COM> wcs@ho95e.ATT.COM (Bill.Stewart) writes:
> } While more RS232 applications use speeds up to 19200 bps, there are several
> } products that talk 115kbps.  ...
> } 
> } How does this work?  Is it RS-422?  ...
> 
> The speed of the serial ports in the PC is set by putting a divisor
> into a latch. The output speed (baud rate) is then base/divisor. For
> the PC the base rate is 115200cps, which can be divided down to most
> common speeds. Most PCs and clones will go 19.2kb cleanly, with error
> rates increasing as you go 38.4kb and 76.8kb.  ...
> 
> Kermit 2.29b should run the windowed protocol at at least 76.8kb, and
> give about 70% efficiency.

    i already knew about the divisor latch and the baud clock, so 19.2K,
38.4K, and even 115K bps are no surprize to me.  76.8K, tho!  i'd really
like to know how you do that on a stock pc serial port!  how do you get
the value 1.5 into the divisor latch?? :-)

	wayne hamilton
	U of Il and US Army Corps of Engineers CERL
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