NES 2.0 Mapper 409

NES 2.0 Mapper 409 denotes the retroUSB DPCMcart circuit board, used for the homebrew music cartridge "A Winner is You" released by retroUSB.. It is basically an extremely oversized version of UNROM that latches twelve bits of the address, rather than the data, bus for selecting banks from a 64 MiB PRG address space.

Banks

• CPU $8000-$BFFF: 16 KiB PRG bank, switchable
• CPU $C000-$FFFF: 16 KiB PRG bank, fixed to last bank
• PPU $0000-$1FFF. 8 KiB CHR RAM, unbanked
• Mirroring: Hard-wired

Registers

Address Latch ($C000-$CFFF, write)

Mask: unknown, probably $8000

A~FEDC BA98 7654 3210
  -------------------
  1... BBBB BBBB BBBB
       ++++-++++-++++- PRG A25..A14 if CPU A14=0

See also

• https://forums.nesdev.org/viewtopic.php?t=15188
• https://web.archive.org/web/20191024003230/nintendoage.com/forum/messageview.cfm?catid=34&threadid=160050