Re: Zip-GS speed and cache

[mhackett@vaxxine.com (Michael Hackett)]

Jim Pittman <casa@unm.edu> wrote:

> I called Digi-Key and they said they had 32-mHz crystals. So I can get
> a new crystal and slow the Zip down to 8-mHz. But -- if it runs okay at
> 9.3 mHz and 8-k cache, am I better off than I'd be at 8-mHz with 16-k?
> Is the odd 9.3 mHz speed likely to cause any problems? (Digi-Key said
> they could not supply a 36-mHz crystal for exactly 9.0 mHz speed.)

The odd speed will not be a problem (mine is running at 8.89Mhz with a
35.5Mhz crystal, as it didn't work at 10Mhz and that was the next
available crystal down), unless your 65816 is only rated for 8Mhz.  My
card was sold as a 7Mhz version, but had a 10Mhz 65816 on it, so we
thought we could push it up, but it doesn't work on either of my ROM1s
(one early original ROM0 model, one later ROM1). :-(

I would try rearranging the cache chips to see if another combination
works, as apparently the chips in the DATA sockets need not be as fast
as those in the TAG sockets.  So, for example, if you move the one in
the second TAG socket (the one labelled 16/64k) to the first DATA socket
(labelled 8/32k) to its left, you might get lucky and find it works.  If
not, then you might look into getting a couple of faster chips for the
TAG and possibly the DATA sockets (from what I've read, it is not
necessary, or sometimes even desirable, to put faster than 45ns chips in
the DATA sockets).

However, I agree with rubywand that you will see a bigger improvement
from increasing the cache than increasing the speed by 1Mhz or so.

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