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From: silver@xrtll.uucp (Hi Ho Silver)
Newsgroups: comp.sys.ibm.pc
Subject: Re: changing AT's clock
Keywords: clock
Message-ID: <1990Jun7.235834.9063@xrtll.uucp>
Date: 7 Jun 90 23:58:34 GMT
References: <9207@hubcap.clemson.edu>
Organization: Not around here, pal!
Lines: 28

In article <9207@hubcap.clemson.edu> snugroh@hubcap.clemson.edu (Anto) writes:
$I just bought a used NEC AT-compatible.
$It has 80286-8MHz.
$When I opened it, it looked like all memory (ROM and RAM) are 
$for 12 MHz. So I wonder if I can just change the CPU and clock to 12 MHz to
$get better speed with cheap price.

   It probably won't work.  There are other items in your system besides
the ROM, RAM and CPU which may be affected.  Chances are all the "glue"
chips will be able to run at the higher speed, but keep in mind that the
I/O bus that feeds the expansion slots probably takes its timing directly
from the CPU's clock, so by speeding up the CPU to 12 MHz, you'd also be
speeding up the expansion slots to 12 MHz and chances are at least one
of whatever cards you have plugged in will not work at that rate.  There's
another discussion in this group on that topic; you might want to read it.

$There are several x-tals in the mother board (the motherboard has serial and
$parallel port), but the one that close to CPU is 24 MHz.
$Anyone know about clock divider by 3 ?

   I'm not familiar with the various chips used to drive 80286s, but I
know on some other microprocessors the crystal frequency was divided by
three.  The 24 MHz crystal is probably the correct one.
-- 
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