INES Mapper 229

iNES Mapper 229 aka "BMC 31-IN-1" is a simple mapper. Writing to anywhere in $8000-FFFF will affect both mirroring and its mapping for CHR and both PRG pages.

Banks

• PRG: 2x16KiB
• CHR: 1x8KiB

Register

Mask $803F, range $8000-FFFF
Address:
%1xxx xxxx xxHP PPPP
              C CCCC
 H = mirroring [0=vertical, 1=horizontal]
 P,C = bits for mapping both CHR and PRG, all pages

This means that both PRG pages will be loaded with the same bank. However, if all M bits are 0, then the second page of PRG gets mapped to 1 instead of 0.

Nestopia does not seem to restrict the CHR banking to the lower five bits, potentially using all 16. Otherwise, Nintendulator does the same.

Sources

• Nestopia implementation
• Nintendulator implementation