Date: Thu, 26 Jan 1995 08:12:22 -0600 (CST) From: Joe Greco <jgreco@brasil.moneng.mei.com> To: hackers@FreeBSD.org Subject: Re-clocking a 16550 for 230,400: Message-ID: <9501261412.AA01346@brasil.moneng.mei.com>
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(taken from a Usenet article I just posted. Reposted here because it seems appropriate): 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
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