PC88 I/O Map

 Found this map with the I/O ports on the PC88 to help with understanding disassembled code:

PC-8801 I/Oマップ (dti.ne.jp)

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MAME debug

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 When it comes to understanding the code, we could just run the ROM files which contain code through a disassembler and try to read it, but it's easier if we can follow the code while it is executing instead of just reading it. That's one thing debuggers can do.  Luckily MAME already has a built-in debugger that can do that. You just need to invoke it with the -debug command line option, so  mame.exe shinobi -debug At the command line is enough. It will open the game and a debugger window, like this:  In the debug window you can see the register values on the left, a disassemble of the code at the center top panel, and the command window on the bottom right corner. The debugger includes the usual functions like execute the code instruction by instruction, set breakpoints, examine memory locations, and so on.  Though it's hard to analyze the code just by watching it execute on a debugger. Typically there are thousands of instructions executed for each frame , so ...
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ROM layout

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