Zip GSX not working with 64 Ko cache

8 posts / 0 new
Last post
amauget's picture
Offline
Last seen: 2 days 10 hours ago
Joined: Jan 3 2011 - 11:34
Posts: 272
Zip GSX not working with 64 Ko cache

Hello to all,

I'm trying to upgrade my Zip GSX v1.02 card with 64 Ko cache.
It is running at 10 Mhz with a 65C816-10. I'm using brand new SRAM UM61256K-15 and UM61256FK-15.

When 64 Ko is configured, the card crash within a minute under GS/OS 6.01. Sometimes, I can't even get it to load.
Without removing SRAM, if I get back to 32 Ko cache (only 2 chips are used), the card is working great.

As the FAQ suggested, I've also tried to mix fast and slow SRAM (thin package UMxxxx-15 for TAG and large package CXK58255P-45 for DATA). Same behavior : works okay at 32 Ko
and crash at 64

According to the FAQ, 15ns SRAM should be enough for that speed.

Has anyone succeeded to upgrade a Zip GXS to 64 Ko cache ?
If so, what is the SRAM reference ?
Thanks a lot.

speedyG's picture
Offline
Last seen: 9 months 3 days ago
Joined: Nov 16 2011 - 07:45
Posts: 2495
Re: Zip GSX not working with 64 Ko cache

According to the FAQ, 15ns SRAM should be enough for that speed.

Thanks a lot.

Helle amauget,

according to what FAQ ?
Please bear in mind that even also memory chips have a spread of specs by fabrication....
The chips you listed are by spec speed of 150 nS.
This spec just means that the chips is guaranteed to accept speed of 150nS -
but some of that chips work faster and just failed the spec. for 120 nS or less....
It seems to me that the person at the FAQ just had very much luck with his chips to be faster than
150 nS.
At the other Hand the availiable pictures at asimov and other places out there display in
most cases for the larger memory options cards equipped with chips of 70 nS!

Bear also in mind that the "glue" electronics in the PALchips adressing that RAM might have a lack
in design resulting to a possible delay at the highbit of the adressing that might result to the
effect you explain ( highbit=low resulting to less delay and working well - while highbit=high
might demand more time to raise the level and causing then mistake - and just even 10 nS might lead
in such case to failure ) and missing one of the other signals in range of valid timing at the protocol of access.....

Did you also read the notes about different versions of the PAL-chips carefully ? i hope you did....

Probably it´s better idea just to switch to faster chips with less than 120 nS ( better even - like
displayed in the pictures ) or less .... maybe 70nS is the real "safe choice".....

My card is also equipped with that 70nS chips and does not make that kind of trouble....

sincerely
speedyG

amauget's picture
Offline
Last seen: 2 days 10 hours ago
Joined: Jan 3 2011 - 11:34
Posts: 272
Re: Zip GSX not working with 64 Ko cache

Hello SpeedyG,

Sorry, I have included the URL at first but it have been lost...
This is the "reference" FAQ. Here is the link to the FAQ.

BTW, I've already ordered 70ns chips.
I will report the result ASAP.

Offline
Last seen: 2 years 6 months ago
Joined: Aug 22 2013 - 19:03
Posts: 27
Re: Zip GSX not working with 64 Ko cache

I have faster chips filling out 64k in mine and it works fine.

amauget's picture
Offline
Last seen: 2 days 10 hours ago
Joined: Jan 3 2011 - 11:34
Posts: 272
Re: Zip GSX not working with 64 Ko cache

Hello wernst,

How much do you mean by "faster" ?

Offline
Last seen: 2 years 6 months ago
Joined: Aug 22 2013 - 19:03
Posts: 27
Re: Zip GSX not working with 64 Ko cache

I'll look this weekend for you, but I think it was the 70ns parts that Reactive Micro used to sell.

(They are the narrow parts, BTW, so my low-effort solution was to use ZIF sockets on each of the cache chips to have a wide socket accept a narrow chip. Been working fine for around 8 years now...)

-Warr

stynx's picture
Offline
Last seen: 11 hours 22 min ago
Joined: Apr 19 2012 - 09:41
Posts: 211
Re: Zip GSX not working with 64 Ko cache

I have repaired and upgraded more than 10 ZIP GSX up to now. My personal experience is that there are some ZIP GSX that will not accept more than 32k of cache. The best way to get the most out of the ZIP GSX is to test not only several Sram ICs but several Oscillators (brands!) as well. There are some differences between different manufacturers of oscillators as well... In the end the oscillator played a major role in how stable a ZIP GSX is. For example: one of the ZIP GSX would not work @ more than 10mhz ... until i used an especially stable 60mhz oscillator that worked like a treat. The same goes with SRAM. Several 12ns and 15ns SRAMS would not work, but a 20ns SRAM would even let me install the whole 64k @ 15mhz. The TAG-ram has to be much faster that the DATA-ram. normally a 55ns-70ns combination will be all right but i usually use 12-20ns for both (DATA&TAG)

In conclusion: Get several different brands of SRAM (55ns or faster) and oscillators (32mhz and greater). The ZIP GSX can be very picky and may get very unstable with minor changes. Normally you would get a ZIP GSX to about 15mhz with 32k without any major problems, everything above can be considered lucky. There are huge differences in the stability of ZIP GSX cards.

BTW: There are 2 TTL-ICS on the card (74F00 and 74F02) that can be swapped with faster chips. I normally use AS or AC(T) parts for that. This might help to get an unstable ZIP to function properly. they have to be unsoldered though... nothing for beginners Wink

-Jonas

amauget's picture
Offline
Last seen: 2 days 10 hours ago
Joined: Jan 3 2011 - 11:34
Posts: 272
Re: Zip GSX not working with 64 Ko cache

Success ! The 70ns chips work flawlessly.

Log in or register to post comments