Posted By
Gaia
on 2003-01-12
|  Disassembly
I certainly will! I've disassembled the ROM myself and now trying to figure out what's happening there.... There's not much useful done yet, but as soon as I achieve something I'll certainly share it with everyone for further analysis.
Interesting thing is that since the 1551 features a 6510 processor, it has got a processor port located at $00/$01 (the ddr and pr registers). The ROM actually seems to rely on it quite heavily (the IRQ routine, for one). It does not have a VIA 6522 unlike the 1541. It was replaced by the so called TIA 6523 tri-port adapter.
I also wonder what the IRQ sources were on a 1551, and how was the ATN line connected (on a 1541 when the ATN line goes low, it generates an interrupt in the 1541 CPU).
If you need the ROM disassembly in its current stage, just drop me a mail!
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