RFC: Re: Problem with COM (fwd)

Gerard Patel gerard.patel at nerim.net
Tue Feb 12 03:32:08 CST 2002

At 10:05 PM 2/11/02 -0500, you wrote:
(original poster)
>I must use 5726, 5760 and 9600. My app need this to work. On 4800
>and 9600 I got error.
>Now nobody is going to convince me there is any software that will make
>a normal 16550a run at 5726

You still don't have access to the world wide web ?
If you have access to Google, search for the following Usenet posting,
for example :

UnHy6.600095$JT5.16435354 at news20.bellglobal.com

If you can't use Google, you could see that this is a common request 
under Windows. quite a few programmers need to access devices
with non-standard crystals, or even non 8251 chips with specific
In this post, you could see that SetCommState accepts any baud 
rate up to 9600 bauds, and that over 9600 bauds the idea is that
the Windows driver should accept values that are inside a +-1% 
interval of the 'correct' value (although the poster says that the
calculation is bugged and works only for negative differences).

The Windows code for the 8251 family is probably always rounding
to the next integer value under 9600, and if the wanted rate falls
to +-1% of the 'normal' value over 9600. As I understand it, the 1%
tolerance is explained because such a small difference don't matter
for asynchronous serial  communication.


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