Mapper Initial State Documentation?

Is anyone aware of a mapper matrix that includes initial state information for each mapper? Using https://www.nesdev.org/wiki/Color_Dreams as an example, this article describes the bank select register, number, and type of banks, but it does not indicate for instance which of the banks is expected to be in place at startup. It does indicate a 74377-type latch is in use which may imply that the power-on state of a 74377 defines the initial mapping. Is this the intent or is initial state defined elsewhere?

Mapper 1 (MMC1) also demonstrates this, with the reset section indicating:

To reset the mapper, which clears the shift register and sets the PRG-ROM bank mode to 3 (fixing the last bank at $C000 and allowing the 16 KB bank at $8000 to be switched)...

This defines the last bank as being exposed at $C000, but does not indicate which of the other possible banks is guaranteed to be the one at $8000. This mode is then mentioned in the register section

3: fix last bank at $C000 and switch 16 KB bank at $8000

Switch 16KB bank at $8000, so the bank is swappable...but when you hit that power button with four PRG ROMs on the cartridge, if you don't touch the MMC1 register at all and jsr $8345, are you jumping into the middle of PRG0, PRG1, or PRG2?

Are these details left out of mapper descriptions because they are truly up to entropy (undefined?) or for any given mapper, is there a certain predictable state that is always in place the moment power is delivered to the cartridge?

Statistics: Posted by segaloco — Tue Dec 10, 2024 11:00 am — Replies 7 — Views 226

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