Just to clarify, I *think* the Z80's /INT is coming from the vector
generator boards, but at a fixed rate. (40Hz sticks in my head, but that
could be wrong.) ...and I think the game timing is set by the /INT rate, so
changing the Z80's instruction rate shouldn't affect the draw time or game
speed *unless* the Z80's is dropping frame rate (ie, not completing it's
main loop before the next video refresh is due). The 'coprocessor' nature
of the VG made it possible to single-step the Z80 and whatnot during
development and maintain an image on screen though.
I also could be completely full of crap (or at least mis-remembering). (To
put this in perspective, when I was messing with the G80 system I sussed out
how the vector generator stuff worked using a Fluke 9010A and got basic
drawing routines working in Al Kossow's simulator that ran on the Mac--
which in turn eventually trickled down in to MAME. So it "has been a while".
;-)
-Clay
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Received on Sat Dec 3 05:18:21 2011
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