INES Mapper 031
iNES Mapper 031 represents a mapper created to facilitate cartridge compilations of NSF music. It implements a common subset of the features used by NSFs.
PRG-ROM is bankswitched in 8 x 4 kB banks from $8000-FFFF. These are controlled by registers at $5FF8-$5FFF like the NSF mapper. The high bank at $F000-FFFF is initialized to the last bank at power-on.
There is no CHR banking, so it is recommended to use 8 kB CHR-RAM with this mapper.
- PRG ROM size: Up to 1024 kB
- PRG ROM bank size: 4 kB
- PRG RAM: None
- CHR capacity: 8 kB RAM/ROM
- CHR bank size: Not bankswitched
- Nametable mirroring: horizontal or vertical, hard wired.
- Subject to bus conflicts: No
PRG bank select $5000-$5FFF
address data 15 bit 0 7 bit 0 ------------------- --------- 0101 .... .... .AAA PPPP PPPP ||| |||| |||| ||| ++++-++++- Select 4 kB PRG ROM bank at slot specified by write address. +++------------ Specify 4 kB bank slot at: $8000 + (AAA * $1000)
The canonical write position for these registers is $5FF8-$5FFF, as used in NSFs.
At power on, the register at $5FFF is set to $FF. Startup code should be placed in the last bank. There is no change to this register on reset.
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