512KB mapper 7 issue

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aquasnake
Posts: 515
Joined: Fri Sep 13, 2019 11:22 pm

Re: 512KB mapper 7 issue

Post by aquasnake »

Mapper7 is quite picky about the rom timing. I tested the original Battle Toads 1/2 and sometimes they were frozen after entering the game.

It is speculated that mapper7 requires 32KB overall switching, so each bank must have the same "STARTUP" and "VECTORS" code segments. Even so, in the switching process, the data line output on this part of the address is not stable, and there is a switch jump that causes interference. Trying to connect 100 ohm resistors in series on CPU D0-D7 may improve this issue
Last edited by aquasnake on Thu Dec 29, 2022 8:33 pm, edited 2 times in total.
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aquasnake
Posts: 515
Joined: Fri Sep 13, 2019 11:22 pm

Re: 512KB mapper 7 issue

Post by aquasnake »

https://www.nesdev.org/wiki/List_of_gam ... of_PRG-ROM

Even the original BATTLETOADS will access non-existent addresses. So the impedance of open bus is different for different hardware, even different emulators. If it is only temporary storage for writing and reading, it can be replaced by RAM. If it is not the above logic, such as writing different values, but reading the transformed ones, additional emulation is required
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