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.

As with BNROM and UxROM, there is no mirroring, CHR bank, or IRQ control; this mapper has hardwired H or V mirroring.

Examples:

• 2A03 Puritans (ROM)
• Famicompo Pico 2014 (ROM)
• RNDM (info)
• Test ROMs (forum post)

Overview

• 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

Registers

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.

References

• Excerpt from readme.txt describing the mapper

Emulator support

• BizHawk r6492
• MESS r30137
• puNES 0.84
• FCEUX r3094
• Nintendulator 0.975
• Everdrive N8 (w/custom mapper)