Re: FAQ-Zip GS upgrade: The 10MHz alternative

[rder@pro-palmtree.cts.com (Richard Der)]

ballwebr@holmes.ece.orst.edu (Brian Ballweber) wrote:
>Richard Der (rder@pro-palmtree.cts.com) wrote:
>: I have a Zip GS that came as a 7/32 and was used at 7MHz for a long
>: time. The board came with a socketed oscillator, so one day I
>: swapped the 28MHz oscillator with a 36MHz one.  The computer booted
>: up at 9MHz.  When the 36MHz osc was replaced with a 40MHz osc, the
>: Zip ran at an amazing 10MHz!
>
>The speed rating of your processor should be printed on it as a -xx
>following the part number, like this:
>
>W65C816-10 (or similar, -10 for 10Mhz, -7 for 7Mhz, etc...)
>
>This is supposed to be the speed it was intended to run at, however
>it is possible to overclock it and still have it work.  Results may
>vary, but you shouldn't need an array of crystal oscs. to find a
>workable one.
 
The problem is that very often the number printed on the processor
is grossly inaccurate. Processors are rated to guarantee to work
at a certain speed and below. According to the original Zip/TWGS
upgrade article in NAUG a few years back (the one Western Design
Center used to send every time you asked about their 65816 line),
this just means they have been tested to run at that speed. They
have not been tested to work at higher speeds, so what you are
doing with the array of oscillators is, in effect, testing it for
the higher speed.
 
The reason I got several oscillators instead of one was simple.
If I just got a 40MHz osc and the processor couldn't make 10MHz
and I didn't have the next slower osc, I would have to revert
all the way back to 7MHz. With many oscillators, I would have
been able to try 9MHz or 8MHz rather than completely give up
(and wait another week for shipping). Besides, for less than a
dollar and a half each, it is worthwhile "insurance".
 
 
>My Zip was originally a 9/32, but I noticed it had a 10Mhz '816 so
>it was trivial to swap the oscs and get a 10/32.  Incidentally some
>standard freq oscs are used a lot for clocking PC motherboards
>(40Mhz, 50Mhz) so you can typically find them at any local computer
>store.
 
Mine originally had a processor ending in -8, meaning it was rated
for 8MHz. It has been running at 10MHz for over a year, without a
single problem.


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