Subject: Re: [stella] Supercharger internals... From: Bob Colbert <retroware@xxxxxxxxxxxxx> Date: Fri, 08 May 1998 07:49:45 -0500 |
At 05:35 PM 5/7/98 -0400, you wrote: >So after looking at this I decided to code up the Supercharger support >so that it pokes 5 memory ACCESSES after an access to f000 to f0ff. >To my surprise all of the Starpath games worked :-) Now, I guess it >could be that these games only use the first two code sequences to write >to RAM or it could be that this is the way the Supercharger really works. >I also fix a bug in the Supercharger emulation so that Bob Colbert's >Stell-a-Sketch and Multi game work. I wasn't poking on writes only >on reads :-) My theory on the Supercharger hardware is that when the SC is write-enabled an access to page $f0 triggers a timer that sets the read/write line on the SC RAM to write for a short period of time while putting the low-byte of the address in an internal register. It takes a couple of cycles for the read/write line to go high, and if an address is accessed within that period of time then the value is stored. I believe there is a small window of 2 or 3 cycles for which the write would be enabled. I used the sta instruction because it's more logical when reading the code. I would guess that other instructions should work too, like inc, dec, eor, etc... Great work btw! When can we download the new version? Later, Bob -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/stella.html
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