NES 2.0 Mapper 406

NES 2.0 Mapper 406 is used for the homebrew game Haradius Zero. It is basically a homebrew TLROM circuit board that connects the MMC3's address lines differently, and saves the high score to flash ROM. The game executes the flash ROM chip's "Software ID" command; if the manufacturer and model ID do not match the expected values, or it detects that WRAM exists, the game replaces the first level with an unwinnable boss fight.

Submapper 0 denotes the 60-pin release of the game (saying "AXR" at the bottom of the title screen). The MMC3's A0 input is actually connected to CPU A1, so that $8000/$8002 rather than $8000/$8001 are differentiated. The Flash ROM chip is a Macronix MX29F040 (manufacturer ID=$C2, model ID=$A4).

Submapper 1 denotes the 72-pin release of the game (saying "INL" at the bottom of the title screen). The MMC3's $8xxx and $Exxx registers are swapped, so that $8000/$8001 enables/disable IRQ generation, and $E000/$E001 write to bank registers. The Flash ROM chip is an AMD AM29F040 (manufacturer ID=$01, model ID=$A4).