INES Mapper 031

iNES Mapper 031 represents 2A03 Puritans, a cartridge implementing a variant of the NSF mapper.

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.

CHR-RAM is provided, but there is no CHR bankswitching.

As with BNROM and UxROM, there is no mirroring, CHR bank, or IRQ control; this mapper is intended for use with an 8 kB CHR-RAM and hardwired H or V mirroring.

Overview

• PRG ROM size: Up to 1024 kB
• PRG ROM bank size: 4 kB
• PRG RAM: None
• CHR capacity: 8 kB RAM
• 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