Re: Zip GS questions

[pubpc1@library.ucla.edu]

eddy@cs.ucdavis.edu (arekusu) wrote:
>Paul Schultz (pschultz@med.wayne.edu) wrote:
>: Check out the FAQ. It will fill in any gaps in the above info that
>: you will need to do the cache upgrade.
>
>A questions I have about Zip upgrades, not in the FAQ:
>
>How do you know if the ASIC will handle speeds greater than ~12 Mhz?
>
>I can't push my 1.02 board past 10Mhz, with 64k of 15ns SRAMs w/ or
>w/o the high speed 740x chips.

When you put 15ns SRAMs into both TAG and CACHE, the Zip becomes very
unstable.  What you have to do is put the 15ns SRAMs into the TAG
sockets and put slower (45ns or even greater, but not TOO slow) SRAMs
into the CACHE sockets.  Try your original chips for the CACHE sockets
and see if it will work.

I have mine working at 13.75MHz with 15ns in CACHE and 45ns in TAG,
but I had to set the DIP config to think there was 16K of cache even
though the Zip has 64K.  I did not need to replace the 7400.

The ASIC can definitely handle >10MHz.  In fact, people have gotten
the Zip 7MHz Zips to work at 9MHz or 10MHz without changing the cache
at all, but each Zip is unique.

-Scott G.