10 Feb
2008
10 Feb
'08
10:51 a.m.
Basically I'm trying to reverse-engineer the
firmware of a couple of
late-80s Alesis HR-16 and HR-16B drum machines. They use a 32kx8 EPROM
for the firmware, a pair of 512kx8 ROMs for the sampled sounds, a big
custom ASIC for the sample playback and an 80C31 for the clever stuff.
I assume the ROM address latch is hidden in that ASIC, and isn't a
seprate '373 or '572 chip If it was, it would be trivial to trace out the
address bit order, of course. Do the ROM data pins connect straight to
the 8031 (without going through the ASIC). At least you could make sure
the data bits are in the expected order.
What aobut using a logic analyser, connected to the EPROM? You could
capture the first few instructions and the addresses _at the ROM pins_.
You can spot jumps, etc and thus work out what the addresses _should_ be
and thus work out which bit ends up on which EPROM pin.
-tony