Re: ZipGSx Upgrade Questions (I've read the FAQ's)

[Rubywand <rubywand@swbell.net>]

Wayne Stewart writes ...
> 
> Rubywand wrote:
> 
 ....
> >      Do not know why anyone would replace a 74F00 with a 74HC00 on an
> > accelerator board. The 74F00 is a much faster gate than the 74HC00.
> > You would think that when speeding up a board you would,
> > if anything, want to move to faster gates. Suggest you leave your 
> > 74F00 where it is until whoever made the recommendation explains it.
> >
> 
> I heard the explanation about why a slower chip
> helped there about 4 or 5 years
> ago but don't recall the details. However I've
> sped up several ZipGSs and always topped out at
> 12 or 12.5mhz till I replaced the 74F00 with a 74HC00.
 ....

     Your experience fits the info from David Empson quoted by Marvin.

     Evidently, the problem with the 74F00 and the new 65C816 relates to
changed input parameters for the 65C816 due, perhaps, to using standard CMOS
for some inputs.

     A 74F00 will deliver a TTL-level "1". In reality, you will usually get
something above this and be able to drive a CMOS input to "1"; but, the
margin for reaching CMOS "1" will tend to be small and more subject to noise
and temperature differences than is desirable.

     Going to a 74HC00 gives up some gate speed. However, it does guarantee a
solid CMOS "1" output.

     The FAQs Accelerator page has been changed to include your ZipGS upgrade
information. Thanks!



Rubywand