User`s guide

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From: Frank M. Lin
014- What Oscillator freq corresponds to what TWGS/ZipGS
operating speed?
For TWGS and ZipGS, the crystal oscillators runs at 4 times the speed of
the 65816. Below is a chart showing osc and corresponding TWGS or ZipGS speed.
Osc Frequency MHz TWGS/ZipGS Speed MHz
28 7
32 8
33.3333 8.3333
36 9
40 10
42 10.5
46 11.5
48 12
50 12.5
55 13.75
60 15
My understanding is that, if you over-clock a CPU. It just won't function.
You can't damage it. As the disclaimer said, do it at your own risk. I have
tried to run my TWGS at 20 MHz, system won't boot at all. No damage.
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015- How do I experiment with different oscillator
frequencies?
Most of the following is from a piece on ZipGS upgrading by Long. It is
also a useful guide for TranswarpGS owners.
The ZipGS can use three types of crystal oscillators: the common 4-pin
"full size" oscillator module (about the size of a 14-pin TTL IC), a 4-pin "half
size" oscillator module (also used on TWGS), or an on-card circuit with a
separate crystal (little 2-pin metal canister). To be able to use a separate
crystal, your ZipGS must have a resistor at R1 and capacitors at C13 and C14.
These three parts are often omitted from Zips which use an oscillator module.
If your accelerator does not have a socket for the oscillator module, you
should probably install one (14-pin for ZipGS; 8-pin for TranswarpGS).
Experimenting with different frequencies will be much easier. (If your ZipGS has
eyelets for a 16-pin socket*, leave the top two pins open.)
On ZipGS boards, only 6 of the 14 socket pins are connected (picture A).
The Ground (GND) pins 1, 4, and 7 are connected together. The Power pins 11 and
14 are connected together; and, pin 8 is the module Output. Full size oscillator
modules use pins 1, 7, 8 and 14 (refer to picture B). Half-size oscillator
modules use the bottom four pins (4, 7, 8 and 11; picture C).