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Hacking NES ROM to use Con 3 instead of Con 1

Started by BigJoeCool, February 11, 2023, 10:15:33 AM

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I'm really new at this. I have a Famicom w/Everdrive and was wondering if there's a patcher that would take a game that uses Controllers 1 and 2 and make it use controllers 3 and 4 instead. I have a cord that plugs into the front expansion port, and it works for most games, but it looks like games that weren't released in Japan have issues sometimes - T & C Surf Designs for example.


Indeed I believe the controller input routines were more heavily regulated for Japanese releases precisely for the expansion port compatibility.
You would have to make ASM hacks for input routines to make them accept input on either D0 or D1 as an input (as Japanese games should do), as opposed to western-developed games which only take D0 (as I understand, D1 wasn't even connected on NES consoles). (or Paperboy which was even more degenerate on the US and EU versions which expects garbage bits on the input port, and expects a 0x40/0x41 response, probably breaking compatibility with clones. Fixed in the JP version.)
If that response doesn't make sense, then it's probably above what you'd be able to do.
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