> It makes no sense that a manufacturer would have 3 MCUs on the board all with > identical code (especially if one of them is a different MCU to the other 2)
Actually, it would make sense if they were of the mask-programmed variety. Custom-masked parts were never cost-effective unless you were prepared to order them in great quantities before making any revisions. It sometimes happened that when companies had two MCU programs, neither of which took up too much of the code space or used all of the input pins, they would fold both MCU programs into one mode-switchable package. This is what I suspect might be the case with Super Real Mahjong Part 2's X0-005, which I believe to be an undumped UPI-41 MCU that serves as an ADPCM player in one place and a keyboard scanner in another.
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