*BSD News Article 41588


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From: jgreco@brasil.moneng.mei.com (Joe Greco)
Newsgroups: comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.comm,comp.os.386bsd.misc
Subject: Re-clocking a 16550 for 230,400?
Followup-To: poster
Date: 26 Jan 1995 08:10:24 -0600
Organization: Solaria Public Access UNIX - Milwaukee, WI
Lines: 36
Message-ID: <3g8agg$19h@brasil.moneng.mei.com>
NNTP-Posting-Host: brasil.moneng.mei.com

I've looked over all the data sheets.  I've looked through a bunch of Usenet
FAQ's.  I've looked at the sources for my OS's serial device drivers.

Problem:  I need a 230,400 bps serial port.

Somebody's suggested solution:  Buy a Hayes high speed serial card, and
	select the "4x clock" option.

My objection:  Very expensive solution, particularly since my OS does not
	yet have driver support for the Hayes card, and it
	would be used in 16550-compat mode.

I'm running FreeBSD 2.0R.

I've looked at the NS data sheets for the 16550 which suggest that a 4MHz or
8MHz clock is fine, and that the maximum speed supported by the part is
256Kbps.  Now, it would seem to me that it would be a trivial hobbyist level
upgrade to toss a 3.6864MHz crystal on an ordinary, everyday PC serial card
to effectively double the clock rate.  I have not (yet) tried this, but I
was suprised that it was not covered in a FAQ, if it is as simple an upgrade
as it seems (I don't see why not).

I am using the Startech 16552 part for most of my serial ports, by the way,
in case it makes a difference.

Has anybody tried this?  Succeeded?  Failed?  Half & Half?  :-)

Since I don't think that this is of particular interest to the average
hacker, followups have been redirected to poster.  I will happily summarize
any answers (and my own results) if there is any interest in this.

... Joe

-------------------------------------------------------------------------------
Joe Greco - Systems Administrator			      jgreco@ns.sol.net
Solaria Public Access UNIX - Milwaukee, WI			   414/342-4847