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From: grege@gold.gvg.tek.com (Greg Ebert)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: How to set serial port to 115k baud?
Message-ID: <1839@gold.gvg.tek.com>
Date: 7 Jan 91 17:31:30 GMT
References: <1991Jan5.034731.15478@d.cs.okstate.edu>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 35


 ong@d.cs.okstate.edu (ONG ENG TENG) writes:
#Any one know how to set a serial port to 115k baud?  I know how to 
#set it up to 9600 baud and do i/o.  But I have seen some software
#use it at 115k.  How do you do it?  Please also provide any
#general serial port hints you have (that is not found in
#Norton's PC Programmer book).
#

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 :

	The maximum operating frequency of the baud generator is 3.1Mhz.
	However, when using divisors of 3 and below, the maximum frequency
	is equal to the divisor in megahertz. For example, if the divisor
	is 1, then the maximum frequency is 1 Mhz. In no case should the
	data rate exceed 56k baud.
	(Reprinted w/o permission)


If you want to play with it anyway, set the divisor to 1. Because you are
exceeding the spec, there is no guarantee that it will work under all
operating conditions. Also, the data rate isn't EXACTLY 115KBps; it's
115.2KBps which is probably close enough.

What, pray tell, are you talking to at this speed ? 

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