Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!mit-amt!rdsnyder
From: rdsnyder@mit-amt (Ross D. Snyder)
Newsgroups: sci.electronics
Subject: Re: PC Crystals
Message-ID: <3805@mit-amt>
Date: 29 May 89 01:05:50 GMT
References: <306@edstip.EDS.COM>
Organization: MIT Media Lab, Cambridge, MA
Lines: 24

To reduce the speed of your PC, the software hack to the operating system
that someone suggested, which simply wastes clock cycles, is probably the
cleanest hack.  However, since this is sci.electronics, you may feel in
the mood for a little digital hardware hacking, so...

You could build a divider circuit based on a counter IC, such as the
74LS163, which could be inserted between the clock oscillator and the rest
of the computer.  With a debounced switch and the approriate logic gates,
you could build a circuit that would cleanly switch between clock
frequencies.  You could use a thumbwheel switch to set XTAL/1, XTAL/2,
XTAL/3, etc.  With a clean circuit, you could probably switch anytime
with no ill effects.

Things to think about include:
1) Power consumption is usually a function of clock speed.
2) Dynamic RAM needs to be refreshed periodically.
3) Serial com functions require precise timing (although ususally provided
	by a xtal on the UART)

Disclaimer: If it ain't broken, don't fix it.  It's probably better to have
a machine that won't let you win games than one that keeps a door from being
blown shut by the wind.

-Ross