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

[a_specto@alcor.concordia.ca (Mitchell Spector)]

"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.

    It's always been more reliable with the DIP switches set to recognize
32K cache instead of 64K though, I'm not sure why. The difference in
speed between 32 and 64K doesn't appear noticeable at any rate, 
though there is a huge difference between my 9/32 ZipGS and 
when running this board as a 12/32.

Mitchell Spector
a_specto@alcor.concordia.ca