Multigame controls...

I fired up the old Z-80 disassembler last night and looked at the code for
Tac/Scan, Eliminator, Zektor, and Space Fury.

It looks like remapping the controls shouldn't be *too* tough. I'm a
little perplexed that Space Fury and Eliminator only make a single read to
some locations though...

For example-- Space Fury. The code only once looks at input port 0xFA.
(0xFA contains the right and left rotate button status.) Doesn't self test
check those inputs too? Seems like if it did there'd need to be at least
two accesses to 0xFA. Odd. Can you read an I/O port address indirectly on
a Z-80?

The main problem I'm forseeing with Space Fury and Eliminator is that I
probably won't be able to do an in-line patch to the code. Since the Star
Trek buttons are on port 0xFC, I need to make a write to 0xF8 to insure I
don't read the spinner knob by accident. Since I've got 48K of code space
(and since SF and EL don't take it all up), I think I'll just jump off past
the end of the game ROM and run my patches there. Shouldn't be too bad.

Tac/Scan and Zektor only read 0xFC about a dozen times each. Tac/Scan at
least looked pretty obvious about what it was doing since there was always
something like:

ld a,ff
out (f8),a
in a,(fc)
...

So swapping thrust and fire there shouldn't be too bad hopefully.

Anyway, it'll probably take me longer to lash the Star Trek control panel
up to the card cage than it'll actually take to make the code changes...
;-)

-Clay

Clayton N. Cowgill Engineering Manager
_______________________________________________________________________
/\ Diamond Multimedia Systems, Inc. clay@supra.com
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Received on Wed Oct 8 10:25:26 1997