Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!vaxb.acs.unt.edu!kenc
From: kenc@vaxb.acs.unt.edu
Newsgroups: comp.sys.atari.st.tech
Subject: Re: 68000 upgrade to a faster 68000 or a 68020?  Fast
Message-ID: <1991Jan7.232807.44220@vaxb.acs.unt.edu>
Date: 7 Jan 91 23:22:07 GMT
References: <CWILLIAM.91Jan7113443@mimsy.umd.edu>
Distribution: usa
Lines: 20

> hardware in general.  It seems to me that I can just pull out my old
> 68000, plop in a new one rated at 16MHz, and then run the 16MHz clock
> line to the new 68000?  For that matter, can I move up to a 68020

Chris,
  This is a no go, because of the way that the CPU and the MMU swap cycles. 
From what I understand, the system clock ALREADY runs at 16 Mhz, but it gives
half to the 68000, and half to the MMU.  (I may have the wrong chip...it may be
the glue...)
  Anyway, since THAT chip, and all the support chips are not rated at anything
like 16 Mhz, and all the timing is sensitive, you try to double the speed of
the system clock, and you have an expensive paperweight.
  I think the speed up kits available use a caching technique, so that the new
chip DOES run at 16 Mhz, for it's cache, and 8Mhz for anything else.  That way,
you do get the speed improvement, and the system timing doesn't change.  Only
problem, is that that usually requires a caching chip, and another
daughterboard, making the cost more than $100.  
  
  If I'm wrong here, please jump in, I'd LOVE to be able to speed up my ST for
<$100....(grin)