Re: Re GS 65816

[supertimer@aol.com (Supertimer)]

buggie@ben14.unm.edu (stephen e buggie) wrote:

>Trevor Mahan is doing a public service to organize this!
>
>I will order one; add me to the list!
>
>My ZIP-GS is  7/64  (7 megs, 64K cache.).
>I bought it new, and have not tinkered with it.  Does anyone know whether 
>there are any complications or increased crashes from doing this mod?
>Somehow, somewhere, I _think_ I read that there are trace modifications
>needed to increase the speed.  II ALIVE (I think) ran an article on
>souping up the ZIP-GS.
>
>I have only one ZIP-GS, and they are no longer in production.  I want to
>adopt a cautious approach on hacking this jewel...

That is a reasonable approach.  However, increasing the speed of the
Zip GS has become a lot easier since the past few years because
the enhanced 65C816 (the Sanyo redesigned 14Mhz part) is a much
better chip.

For Zip GS users who do not want to hack the card itself, it is quite
easy to boost the speed by simply changing the CPU and changing
the oscillator.  The oscillator is the metalic box on the card.  You
replace it with one that has 4x the Mhz rating that you want to clock
the CPU.  So right now, you have a 28Mhz oscillator.  The CPU is
easily identified by the numbers 65C816 printed on it.  There are two
of these (one the old IIGS CPU stored on the card)...you are interested
in the PLCC (the square shaped) one.

Cache speed and size on the Zip GS influences maximum CPU
speed.  If you can't run your Zip GS at a faster speed, the solution
is to drop down in increments to 32k and then 16k of cache.  Just
change the DIP switch settings (you don't have to change chips...
64k of cache can be set to any of the cache size settings).  For
example, if your Zip 7/64 is stable at 8Mhz in the 64k cache
setting, setting the cache to 32k will likely make it stable at 9Mhz.
Setting it to 16k will likely make it stable at 10Mhz or even 12.5Mhz.

As for the trace modifications, they involve modifying the sockets
on the Zip GS to take the less wide cache memory chips.  The
Zip GS is built to take 6 mil wide chips but the faster memory
chips are all 3 mil wide because that's what PC motherboards
take.  The modification involves soldering in a row of socket
pins in the middle of the memory sockets to accomodate the
smaller chips.  This is how people get 15/64 Zips.  If you don't want
to mess with this (unlikely from the BUG-ventor ;-) there's also
socket adapters.  These plug into the wide socket and provide
a 3 mil wide socket for the memory chip to plug into.  They cost
about $7 each.  These are worth it for piece of mind if this is your
only accelerator.

I use a TWGS card that I modified to 12.5Mhz (TWGS cards are
easier to modify in that they can usually be bumped to 12.5Mhz
with only a CPU and an oscillator change.  No need to change
settings or memory chips most of the time).

The difference between 7Mhz and 12.5Mhz makes a big difference.
The IIGS is like a new machine again.