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From: ong@d.cs.okstate.edu (ONG ENG TENG)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Change clock speed on 386SX motherboard?
Message-ID: <1991Jan15.222135.2964@d.cs.okstate.edu>
Date: 15 Jan 91 22:21:35 GMT
References: <4610@altos86.Altos.COM>
Organization: Oklahoma State University
Lines: 37

From article <4610@altos86.Altos.COM>, by rcollins@altos86.Altos.COM (Robert Collins):
> In article <1991Jan5.192547.20804@d.cs.okstate.edu> ong@d.cs.okstate.edu (ONG ENG TENG) writes:
>>> As I mentioned before, just got a 16MHz 386SX.  In the manual, it seems 
>>> to be saying that the same motherboard (merely refered to as NEATsx
>>> motherboard, manual prepared by a technical documentation company) can
>>> be used as a 16MHz or 20MHz.  Can it be true that I merely has to
>>> change the CPU from a 386SX-16 to a 386SX-20 and speed the RAM
>>> up appropriately, add the 40MHz oscillator (for the 20MHz CPU, as 
> 
> The hardware probably will handle it, but the real question is will the
> peripheral bus handle it?  The NEAT chipset can drive the bus in two
> different manners:  1) it can run syncronously to the system clock as
> SYS_CLOCK / 2, SYS_CLOCK / 3, etc.  or 2) it can run asyncronously
> from a separate clock crystal.  If your computer runs the bus 
> asyncronously, then you have it made in the shade. 

Hhhmmm... I thought the discussion ended two centuries ago.
Well, my NEATsx chipset motherboard allows use of an optional
crystal for 20MHz operation.  This is set via a shorting block on the MB.
My only concern now is the heat.

Well, since we are here, I might as well make an update since I got
help from so many people, some of whom themselves are interested in doing
the same.

I have ordered 3 crystal oscillators from Digi-Key few days ago.  One
35Mhz (for 17.5MHz operation) and two 40MHz (for 20MHz operations) of 
different casing (I don't know which will fit).  I also ordered a good-size
heatsink, but they no longer carry any heat-resistant glue.  Hopefully
the local Radioshack carries some else I am up the creek w/o a paddle.
(Anyone care to send me some, I promise not to sue if my motherboard
blows up, ha, ha).  Another would be that the MB and CPU is actually
built for 20MHz operation and that heatsink is not needed.

Let you know after the surgery.

E. Teng Ong (ong@d.cs.okstate.edu)