INES Mapper 038

iNES Mapper 038 represents the board used for Crime Busters. It is another mapper very similiar to GNROM (66) except the bits and writeable port moved around.

In Disch's style:

 $7000-$7FFF: [.... CCPP]
  P = Selects 32kB PRG @ $8000
  C = Selects 8kB CHR @ $0000

Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The 74138 used by this board uses /PRGSEL and R/W on its enable inputs, but /PRGSEL is 1 while M2 is low, not just while M2 and A15 are high. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the 74161's /LOAD line will still load from the data bus.

Emulator oversize support:

 FCEUX (2.1.5):
  $7000-$7FFF: [CCCC CCPP]

 Nestopia (1.4.0h):
  $6000-$7FFF: [CCCC CC..]
               [PPPP PPPP]