Looks like a bug in the cpu where it first does the decimal adjust which triggers a flip in the high bit and somehow interprets that as an overflow.

hmmm, looking at regular 6502 ADC implementation (http://git.redump.net/cgit.cgi/mess/tree/src/emu/cpu/m6502/ops02.h#n312) it seems to give the results you're seeing....or am i missing something??

Last edited by judge; 03/10/10 07:14 PM.