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On Oct 29, 2005, at 7:00 AM, richard jackson wrote:
Didn't know there were a 1.7 ROM. Thought you had to
upgrade the cache to 32K to attain speed over 10MHz.
1.7 ROM was for 8k cache.
1.8 ROM is for 32k cache
the 1.8 has the code to access the 32k. It is 65816 code, so the CPU
on the TWGS not only runs as the the Apple IIgs CPU, but the CPU also
takes care of cache logic and perhaps slowdown logic.
I've run 5 different TWGS boards at 12.5mhz with the 1.7 ROM and 8k
cache. The cache does speed things up (I also have a 32k cache
board), but it is independent of the CPU speed.
There used to be the need for GAL chips of a certain version to run at
faster speeds. The first batches of 20mhz 65816 had faulty
engineering. Running certain instructions at high speed would crash
the processor. The GAL chips on the TWGS got around this by slowing
the CPU down when the sensitive instructions were encountered.
I wonder if the TWGS board will run its fastest with no GALs
installed. I'll have to try removing them one of these days and see
if it runs any faster. I'm pretty sure they are all wired in
parallel, and it doesn't matter which location you have them plugged
into.
Rich
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