Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!sco!md
From: md@sco.COM (Michael Davidson)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: How to set serial port to 115k baud?
Message-ID: <9493@scolex.sco.COM>
Date: 9 Jan 91 08:19:19 GMT
References: <1991Jan5.034731.15478@d.cs.okstate.edu> <1839@gold.gvg.tek.com> <3815@ns-mx.uiowa.edu>
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Organization: The Santa Cruz Operation, Inc.
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In article <3815@ns-mx.uiowa.edu> williams@umaxc.weeg.uiowa.edu.UUCP (Kent Williams) writes:
>In article <1839@gold.gvg.tek.com> grege@gold.gvg.tek.com (Greg Ebert) writes:
>> ong@d.cs.okstate.edu (ONG ENG TENG) writes:
>>#Any one know how to set a serial port to 115k baud? 
>>My 16450 data sheet says you can't do it. The AT runs the 16450 with a
>>1.8432Mhz clock, which is 16x 115Kbaud. Thus, the divisor in the 16450
>>is 1 (unity). But, the sheet says :
>>
>> S T U F F   D E L E T E D
>>
>>If you want to play with it anyway, set the divisor to 1.
>
>You can't run asynchronous communications with a divide by 1.  

Read what Greg wrote!! (and a 16450 data sheet!) The clock frequency
in this case is 1.8432Mhz - loading the 16450 divisor latch with a
value of 1 gives an effective divisor of 16 - that's just the way the
divisor latch is implemented on the 16450 ....

You *can* run a 16450 at 115.2K bps but your mileage will certainly
vary - the 16450 or 16550 will probably hold up OK but you may have
some problems with with the RS232 drivers - and don't expect to get
away with more than a few feet of cable at that speed.

I regularly run a Sharp JX100 color scanner at 57.6K bps on a standard 
PC dumb serial card which has been upgraded from a 16450 to 16550.
I have also successfully run it at 115.2K bps - I don't usually run
it at 115.2 simply because the scanner itself can't actually make
full use of that bandwidth and the link is certainly more error prone
at that speed.