Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!um-math!sharkey!aucis!easton
From: easton@aucis.UUCP (Jeff Easton)
Newsgroups: comp.sys.m6809
Subject: Re: fast clock for 6809
Summary: Not exactly...
Message-ID: <410@aucis.UUCP>
Date: 2 May 89 01:31:37 GMT
References: <1605@ccnysci.UUCP> <1984@wpi.wpi.edu>
Organization: Andrews University, Berrien Springs, MI
Lines: 43

In article <1984@wpi.wpi.edu>, jhallen@wpi.wpi.edu (Joseph H Allen) writes:
> In article <1605@ccnysci.UUCP> jhuang@ccnysci.UUCP (Jian Huang) writes:
> >
> >version available? We ran that chip at 3 mhz wihtout any
> >problem. But I don't know the long-term effect to the
> >system. Does anyone have such experience on this?
> 
> I think it's safe for the processor to do this (you have to go quite fast for
> the processor itself to start screwing up (I've seen 1Mhz parts run at 2Mhz)).
> But, take a look at the bus timing:  The set-up and hold times remain the
> same no matter what speed the processor is running at.  So if you increase the
> processor speed, the peripheral access time must be much faster than if you
> used a higher speed part at that same speed. 


Whoa! hold the phone!

  Remember that that 2 Mhz 68B09 is the *exact* same part as that 1 Mhz
6809.  The only difference is that the 68B09 has been tested for a 2 Mhz
speed and has been rated to run at said speed.  The setup and hold times
of the 1 Mhz part are spec'ed assuming that the main clock is indeed
running at 1 Mhz.  If you take that 1 Mhz part and run it at 2 Mhz (and
it manages to run at that speed) then your effective setup and hold times
are the same as the 2 Mhz part.  Mind you, Motorola wont guarantee that 
that 1 Mhz part will meet the 2 Mhz spec's, after all, thats why they
sell a 2 Mhz version.  They guarantee that their 2 Mhz version will meet
their published spec's.

  Moral of this story,  The 2 Mhz chip is the same die as the 1 Mhz
version, its just been tested and guaranteed to work reliably at
2 Mhz.  You can proably take a 1 Mhz part and run it at 6 Mhz.  You would
proably need a heatsink on the chip and even then, all the other peripherals
proably wouldn't keep up with it.

  Notice that I have never tried the above, I only think it would be neat
to try.  In college someone once boasted that they took a SWTP 6800 machine
up to 12 Mhz before it quit.  The first part to die was a 6850 ACIA.

	-Later
	Jeff Easton
	Zenith Data Systems

OS-9 on a 6 Mhz 6809 system would be awsome. :>