Re: Zip GSX-- speed/cache upgrade

[Rubywand <rubywand@swbell.net>]

"Charles J. Sarchet" writes ...
> 
> I have a Zip GSX 9/32.  About six years ago I had modified one of
> these up to 14 Mhz and a 64K Cache.  Anybody out there still have the
> plans to do this and where to get the parts at?
 ....


     The info below from the newsgroup FAQs file Csa2ACCEL.txt should
help.
 
>>

From: Scott G.

019- How can I modify my ZipGS for more cache and more speed?

     The process described below is very simple. It aims for a speed of
12.5MHz (or better) with 64k cache. 

     First, you will need one of the new Western Design Center 14MHz
65C816's. Alltech Electronics stocks the WDC65C816-14MHz for $20.
Students, teachers, and professors can order the IC in single quantities
directly from WDC for around $7.

     Adaptors: Nearly all of the newer, faster 32k x 8 SRAMs are in
skinny 300-mil packages. If you would rather not modify your ZipGS for
the skinny SRAMs, Digi-Key stocks 300-mil to 600-mil adapter sockets for
about $7 each. The ones you want are part number A502-ND.  You can plug
a 28 pin SRAM into the 300-mil adapter socket and the adapter in turn
plugs into the 600-mil socket on the Zip. (If you have some spare
sockets lying around, you can build your own cheap, but that's another
story.)

     2-4 32k x 8 SRAM chips: There are many sources for 32k x 8 SRAMs
and several types that will work. I got mine (HM62832-15, $5 each) from
JDR Microdevices. You'll want 15ns in the Tag RAM sockets. Up to around
12.5MHz, you want 70ns or faster Data RAM. If current cache size is 64k,
your old TAG RAM chips will, usually, work as Data RAM and can be
transferred to the Data sockets. Otherwise, go ahead and get two
25ns-35ns 32k x 8 SRAM chips for the Data RAM.

     Data RAM should always be slower than Tag RAM. Barry Rees posted
his experiences on this matter (that Data should be significantly slower
than Tag) and I found that the original Tag chips were fast enough.

     A "full size" oscillator module: Digi-Key, JDR, Mouser, ... have
these.  Divide oscillator speed by four to get Zip speed. JDR has the
OSC50.0 (50MHz oscillator), which will make a 12.5MHz Zip. The
oscillators are cheap enough to get two or three for experimenting with
higher speeds.
   
     So, you just plug your Tag and Data RAM chips into the Digi-Key
adapters and plug the adapters into the Tag and Data sockets of the Zip.
Then, you install the new 65C816 and oscillator and make sure DIP switch
1-7 and 1-8 are both set OFF (for 64k cache). That's it, done completely
without soldering.

     ZipGS boards vary. On some you may be able to go above 12.5MHz by
just plugging in a faster oscillator. On others, you may have to choose
between getting faster Data RAM or settling for a lower speed. The new
65C816 is rated for 16MHz and many users have gone to 14MHz and above.
For speeds above 12.5MHz, the usual recommendation is to get Data RAM
rated at 35ns or better.

     For a step-by-step guide, download my ZipUpgrade.SHK HyperCard
stack at ...
ftp://ground.ecn.uiowa.edu/apple2/apple16/Hypermedia/Hypercard/ . 

<<


Digi-Key (800-344-4539; http://www.digikey.com) IC's and general parts
supplier

JDR Microdevices (800-538-5000; http://www.jdr.com ) Apple II and
general parts supplier

Mouser Electronics (800-346-6873; http://www.mouser.com ) major IC and
general parts supplier



     For additional info (e.g. on experimenting with different
oscillator frequencies and converting sockets for skinny RAM) see
Csa2ACCEL.txt at ...

for Viewing via an FTP program or for downloading ...
 ftp://ground.ecn.uiowa.edu/apple2/Faqs/

for on-line perusing via Netscape, etc. ...
 http://www.grin.net/~cturley/A2.FAQs.and.INFO/CSA2.FAQs/
 ftp://apple.cabi.net/pub/applegs/FAQs.and.INFO/A2.Csa2.FAQs/
 ftp://ground.ecn.uiowa.edu/2/apple2/Faqs/Formatted/ (double-spaced)



Rubywand