INES Mapper 081

N715021

Company	NTDEC
Complexity	Discrete logic
Boards	N715021
PRG ROM capacity	64K
PRG ROM window	16K + 16K fixed
PRG RAM capacity	None
CHR capacity	32K
CHR window	8K
Nametable mirroring	Fixed H or V, controlled by solder pads
Bus conflicts	No
IRQ	No
Audio	No
iNES mappers	081

This mapper is used on exactly one known game: Super Gun from NTDEC. Although the game's bankswitching code seems to suggest two separate data latches at $6000 and $8000-$FFFF (the latter with bus conflicts), the board actually latches the four lowest address bits, and ignores the write to $6000.

Banks

• CPU $8000-$BFFF: 16 KB switchable PRG ROM bank
• CPU $C000-$FFFF: 16 KB PRG ROM bank, fixed to the last bank
• PPU $0000-$1FFF: 8 KB switchable CHR ROM bank

Registers

PRG/CHR Bank Select ($8000-$FFFF)

 CPU address bit#
1111 1100 0000 0000
5432 1098 7654 3210
---- ---- ---- ----
1... .... .... PPCC
               ||||
               ||++------ Select 8 KB CHR ROM bank for PPU $0000-$1FFF
               ++-------- Select 16 KB PRG ROM bank for CPU $8000-$BFFF

Related

Discussion with PCB images and analysis as well as Kazzo duping script