INES Mapper 099

Mapper 99 is a simple mapper used by Vs. System games such as Vs. Super Mario Bros. It is comparable to CNROM, but without bus conflicts.

Registers

Controller and CHR ROM bank ($4016)

7  bit  0
---- ----
xxxx xCxS
      | |
      | +- 1 then 0: Request a report from the controller ports
      +--- Select 8 KB CHR ROM bank for PPU $0000-$1FFF
           Note: In case of games with 40K PRG-ROM (as found in VS Gumshoe),
                 the above bit does additionally change 8K PRG-ROM at $8000-$9FFF.

The Vs. System has other ports related to coin insertion and DIP switches that must be emulated to get games to advance past attract mode, and most games' palettes differ from the standard RGB NES palette used by Duck Hunt and PlayChoice games. See Vs. System for more information.