INES Mapper 031

NSF subset

Company	varies (homebrew)
Complexity	CPLD
Boards	unknown (homebrew)
PRG ROM capacity	1024K
PRG ROM window	4K
PRG RAM capacity	None
CHR capacity	8K
CHR window	n/a
Nametable mirroring	Fixed H or V, controlled by solder pads
Bus conflicts	Not applicable
IRQ	No
Audio	No
iNES mappers	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 (ROMs)
• RNDM (info)
• EZNSF (forum post)
• ZENSF (forum post)
• Test ROMs (forum post)

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 1.11.2
• FCEUX 2.2.3
• MAME 0.162
• Mesen 0.9.0
• Nintendulator 0.975
• OpenEmu (FCEUX core) 2.0.3
• puNES 0.84

Cartridges:

• Everdrive N8 OS V14
• InfiniteNESLives Mapper 31 board