Re: SRAM on ZipGSX - how fast for 14MHz?

["Rodney Hester" <rod3@mindspring.com>]

"Mitchell Spector" <a_specto@alcor.concordia.ca> wrote in message
3b61c718.9013498@newsflash.concordia.ca">news:3b61c718.9013498@newsflash.concordia.ca...
> "Rodney Hester" <rod3@mindspring.com> wrote:
>
> >Right now I'm trying to push a ZipGSX to 13.75 MHz with a 55 MHz
oscillator.
> >I've already done the 74HC00 mod successfully.  I'm running 15ns tag RAM
and
> >20ns data RAM, with zero stability.  It won't even finish booting.
Swapping
> >for a 40 MHz oscillator (the next closest I've got) cleans up everything
> >nicely, as does (usually) putting both 15ns SRAMs in the first (32K)
banks,
> >flipping the jumper to 32K cache, and cranking down the speed a notch or
two
> >with the Zip CDA while running the 55 MHz oscillator.
> >
> >Should I have purchased even faster SRAM?  I can get 12ns chips, but I
think
> >that's the fastest that is readily available.  For those who have a
ZipGSX
> >running comfortably at 14 MHz, what speed SRAM are you using?  I'd just
like
> >to try to gauge if I'm encountering a non-SRAM problem here.
>
>     With my 15 MHz/64K cache ZipGS I have 45 ns (wide) SRAMs in the
> Data sockets and 15 ns (narrow) in Tag. From what I remember, it was
> actually beneficial having *slower* memory for the data area of cache.

I've found that putting the 45ns wide SRAM chip I have in the data socket
(and switching the jumpers to 32K cache) does indeed allow me to run
somewhat reliably at 13.75MHz, but the system will eventually lock up or
crash.  From what I've read, 30ns SRAM is pretty much required in the
worst-case scenario, which is why I thought 20ns would be perfect.

It appears that brand matters at least as much as speed.  If anyone has a
known, reliable source for reasonably fast SRAM that can be _tested good_ on
a Zip GS at 14MHz, I'd like to talk to them about purchasing some data RAM.
I know a gentleman that worked for the company used to provide this service
(David, I believe it was?), but I can only assume that is no more.

Rodney