Re: Zip GSX Mod to 12.5Mhz (or better)

[Polymorph <mike.a.stephens@gmail.com>]

scott wrote:
> In article <C31BF953.4D3D%bjjlyates@bellsouth.net>,
> winston19842005  <bjjlyates@bellsouth.net> wrote:

<snip>

>
> I used 12-ns SRAM for both tag RAM and cache on mine, so it has the 
narrow
> chips all across.  Then again, I think I paid nowhere near $12 per 
chip for
> it...JDR isn't exactly the cheapest place to buy this stuff.
>
> I've had trouble in the past getting it to run reliably beyond 8 MHz,
> though, even with a 14-MHz processor and with whatever 74Fxx parts are
> supposed to be replaced with 74ACTxx.  With the upgraded power supply 
that's
> in there now, I might give it another shot...just need 40- and 50-MHz
> oscillators to give 10 and 12.5 MHz operation another shot.


Scott,

I read in a couple of places that in order for the upgrade to work, the 
DATA SRAMs needed to be considerably *slower* than the TAG SRAMs. Now I 
have no idea why this is, but it might be your problem? This is exactly 
why the hypercard stack specifically says to use 70ns SRAMs for the 
DATA. It also allows for an easier upgrade as .6" chips are still 
available at this speed. It also says that 12.5Mhz should be obtainable 
for just about everyone using this method. YMMV with faster speeds 
however. When I get some more crystals, I'll try pushing mine board a 
bit faster and see what I can manage.

The other thing I should point out (as its a bit misleading), the prices 
I have listed on my web site is the total cost for all of a particular 
part. So the US$11.98 that I've listed is for *both* the 12ns SRAMs.  I 
probably should put a note on my web site indicating this - my bad. 
There may be other places cheaper, but JDR was previously mentioned and 
they had just about everything I needed (which is important when 
shipping to Australia as you want to minimise the shipping cost).

cheers,
-p