INES Mapper 218
iNES Mapper 218 is used by the homebrew game Magic Floor. Excluding the CIC, the cartridge board only contains a single PRG-ROM chip (up to 32KiB).
There is no CHR-ROM or CHR-RAM on the cartridge. Instead, the console’s internal 2KiB nametable RAM is mapped as CHR-RAM. This RAM is permanently selected (CIRAM /CE wired to GND), and can be used in four configurations by wiring CIRAM A10 to one of the PPU A10..A13 address lines:
| CIRAM A10 connection | Effect on PPU nametables | Effect on PPU pattern tables | iNES Flags 6 | UNIF “MIRR” bit 7-0 |
|---|---|---|---|---|
| PPU A10 | Two-screen, Horizontal arrangement (“Vertical mirroring”) | 2KiB (128 tiles) CHR-RAM, also mapped to nametable data | $A1 (0001) | $01 |
| PPU A11 | Two-screen, Vertical arrangement (“Horizontal mirroring”) | 2KiB (128 tiles) CHR-RAM, also mapped to nametable data | $A0 (0000) | $00 |
| PPU A12 | Single-screen arrangement | BLK0: 1KiB (64 tiles) CHR-RAM, “swappable” via PPUCTRL | $A8 (1000) | $02 |
| PPU A13 | Single-screen arrangement | BLK1: 1KiB (64 tiles) CHR-RAM | $A9 (1001) | $03 |
Notes:
- The “alternative nametable layout” (bit 3) in Flags 6 of the iNES header is used to denote the two Single-screen configurations.
- If reads/writes to mirrored addresses are avoided, software for this mapper can also be made compatible with AxROM ($A8,$A9), BxROM ($A0,A1), NROM + CHR-RAM, or other suitable mappers. Magic Floor itself is well behaved enough to be emulated as AxROM or NROM + CHR-RAM with vertical mirroring.
Games:
- Magic Floor ($A8)
- Starfight ($A8)
Tests:
- OAM corruption stress test ROM ($A0)
- Coredump tool v1.7 ($A8)
Miscellaneous: