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From: cyang%peruvian.utah.edu@cs.utah.edu (Cheng Yang)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: AMD Math Coprocessor again.
Message-ID: <1990Dec19.121014.3338@hellgate.utah.edu>
Date: 19 Dec 90 19:10:14 GMT
Organization: University of Utah CS Dept
Lines: 36


Hi, everybody.  I am very thankful that I have got a bunch of helpful
replies from you regarding to the AMD 80C287.  I just called the dealer
and I have another problem.

On the manual of my motherboard, it said that "  To determine which speed
80287 is needed, purchase the one that can operate at 2/3 the maximum speed
of your motherboard.  The IBM AT computer is designed to use the pin on the
80287 that devides the crystal frequency by 3.  The 80286 devides the crystal
frequency by 2 to obtain the system clock speed. .... "  and it recommend I
use 80287-10 to work with my 16MHz 80286.  Actually the crystal frequency
on my motherboard is 32 MHz.  So the coprocessor will get 10.67 MHz.(not
exactly 10 MHz)  (My motherboard is bought over one year ago and there
was few 12 MHz coprocessor at that time, I think.)

The dealer I talked to said that I need an AMD 80C287-12 which is $139.00.
And he said that the $99.00 AMD 80C287 is 10MHz and it is for 12 MHz 286 or
less..

My question is:  Who is right?  My manual or the dealer.  What will the result
be if I put that 10MHz AMD 80287 on my motherboard, will the 10.67MHz hurt
the 10MHz 287? Or the chip won't work totally?    Do I really need a 12MHz
coprocessor???

I will be very appreciated if you can give some advice.

Thank you very much for your time in advance.

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*	Ho capito, signor,si!........                                       *
*                                                                           *
*Cheng Yang				Home Address:                       *
*Department of Computer Science		808 East, 300 South, #3             *
*University of Utah			Salt Lake City, UT 84102            *
*E-Mail Address:cyang@peruvian.utah.edu	Tel: 801-322-1918                   *
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