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From: mjg@ecsvax.UUCP (Michael Gingell)
Newsgroups: net.micro.pc
Subject: Re: 80287 and the IBM AT
Message-ID: <1996@ecsvax.UUCP>
Date: Thu, 4-Sep-86 08:46:27 EDT
Article-I.D.: ecsvax.1996
Posted: Thu Sep  4 08:46:27 1986
Date-Received: Fri, 5-Sep-86 19:44:04 EDT
References: <3312@utcsri.UUCP>
Distribution: net
Organization: UNC Educational Computing Service
Lines: 20

> I heard recently that the 80287 runs at a clock speed of only 5.3 MHz when
> in an IBM AT and also that one can purchase a small board which fits into the
> 80287 socket on the AT, to drive it at 8 MHz (assuming of course one has an
> 80287-8). Where can one purchase such a board? Any information would be
> appreciated. If you have them, please include prices.
> 
The 80287 runs at 1/3 of the system clock while the processor runs
at 1/2.  On 6 and 8 mHz machines this gives speeds of 4 and 5.33 MHz
respectively for the coprocessor clock.

The 80287 is designed to be able to run asynchronously from the 80286
clock however. You can attach an 80287 running at 10 MHz simply by
plugging it into the socket provided BUT giving it a separate clock
signal. You can get plug in modules that do this from Microway and
Hauppauge with speeds from 6 to 10 MHz. All they do is interpose
a socket which breaks the clock supply from the motherboard and then
provide their own clock. You must have the correct (approx 2:1)
clock duty cycle though.

Mike Gingell ...decvax!mcnc!ecsvax!mjg