Date   : Wed, 18 Mar 1992 07:37:48 GMT
From   : mcsun!uknet!strath-cs!st-and!mde@uunet.uu.net (Matthew Emberson)
Subject: Re: Z80 chrystal upgrade ???

I have had a number of Z80As running at 6 or even 8 Mhz. At times I run out
of Z80Bs and have to use a Z80A as a temp measure. The problems you can get
tend to be random, infrequent and  usually terminal. In most cases if a Z80 is
to fail at the new speeds, you find out in 3 or 4 seconds after trying it.
One point to note. If the clock speed is incresed, the actual speed of a system
may be slower. Someone said recently that they designed circuits using memory
that just met the Z80 timing specs. If you are using wait states in the cicuit,
a small increase in speed may actaully require you to add an entire wait state
and hence slow the system down!!!. A small point I know, but if you have to 
find this one out the hard way it takes hours.

Also a question. ---  Has anyone done this with a Z80B if so is there a limit
due to heating as I have been told - I don't like destructively testing Z80s.?