> The "FIXED BITS" message is not at all mandatory. It's just a helpful diagnostic > produced by MAME's romcmp tool, which can only catch a few types of common dumping > errors. Depending on the hardware, some romcmp errors might not even be errors: > oversize ROMs are common and graphics ROMs and bipolar decoding PROMs might not need > all the data outputs that the part has. > > A few types of dumping errors romcmp can't detect but have occurred: > > > One or two bad bits (as in Sky Army). > Fixed bits that extend only through certain areas of the dump. (I've patched a few > cases of this by hand.) > Bridges between address lines that cause 3/4 mirroring (as happened with the Eeekk! > color PROM). > Faulty internal latches on 8048, 8041 or related MCUs.
doesn't detect combinations of data lines shorting each other out either (which happened on a recent dump from Sean, that I thought was encryption at first)
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