Subject: Re: 65816 14 meg Western Design chip for GS
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Date: 21 Sep 1999 03:58:48 GMT
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buggie@ben08.unm.edu (stephen e buggie) wrote:

>I've obtained the 14 meg Hz square 65816 Western Design  fast processor.
>
>I want to install it in my ZIP-GS  7/64 accelerator card.
>
>What needs to be done?  How do you pop out the old chip from its socket on
>the ZIP-GS?   Do other changes need to be done????
>
>Any complications likely???   Somehow, it seems too simple that
>acceleration will be achieved merely by popping in a faster chip!  Do
>oscillators etc. need also to be changed???    ZIP-GS experts, PLEASE
>EXPLAIN!

Hi Dr. Buggie, what you do is wiggle the old CPU out with a
bent paper clip or gently use a soldering pick to do the same.
GENTLY so as not to crack the PLCC socket.  Then plug in
the replacement.  You'll then need to change the oscillator.
As you can see, you now have a 28Mhz oscillator.  The
oscillator is 4x faster than the CPU.  It is the CPU's master
clock.  Thus, you want to replace the oscillator with one
4x the speed you want your CPU to run at.

32Mhz oscillator = 8Mhz Zip.  36Mhz = 9Mhz Zip.
40Mhz = 10Mhz Zip.  50Mhz = 12.5Mhz Zip.

When you get the oscillators, you'd then test.

First try replacing the current oscillator with the 36Mhz
one for 9Mhz.  I'm almost certain this will work.
After replacing osc, turn on the IIGS and use it some.
Is it stable?  If so, power down the IIGS and replace
with 40Mhz oscillator for 10Mhz speed.  Repeat.  If
it works, try the 50Mhz oscillator for 12.5Mhz.  If it
works, then great!  You've almost doubled the speed of
the Zip!

If it maxes out below 12.5Mhz, it might be the
cache RAM chips.  Short of replacing the chips,
there is another way to make them work with higher
speeds.

First, identify your current cache size.  This is
identified by DIP switches 7 and 8 on bank 1.

1/7          1/8
on          on              = 8k
on          off              = 16k
off          on              = 32k
off          off              = 64k

It turns out that the Zip GS cache that can't take
a certain fast speed will usually take that fast
speed if you reduce the size setting of the DIP
switches.

For example, if you have a 64k cache and it works
at 8Mhz and 9Mhz but does not at 10Mhz, reduce
cache size setting to 32Mhz and try again.  To get
12.5Mhz, you might have to reduce the setting to
16k.

Will this affect performance?  Only if you drop to
below 16k, it looks like.  Mhz increases usually
mean more until you drop below 16k.  Then the
cache will outweigh Mhz increases.  So as long
as you can get the thing going at the desired Mhz
without dropping the setting below 16k, go for it!

This is pretty obvious when you look at the Zip GS'
competitor, the TWGS.  The TWGS comes with
8k cache standard and is expandable to 32k
cache.  AE never bothered with trying to get it to
64k because the difference is not really worth it.