INES Mapper 038

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iNES Mapper 038
Company Bit Corp.
Games 1 in NesCartDB
Boards UNL-PCI556
PRG ROM capacity 128K
PRG ROM window 32K
PRG RAM capacity None
CHR capacity 32K
CHR window 8k
Nametable mirroring V(hardwired)
Bus conflicts No
IRQ No
Audio No
iNES mappers 038
NESCartDB
iNES 038

iNES Mapper 038 represents the board used for Bit Corp.'s Crime Busters. It is another mapper almost identical to GNROM (66) except the bits and writeable port moved around.

Registers

Bank Select ($7000-$7FFF)

7  bit  0
---- ----
xxxx CCPP
     ||||
     ||++- Select 32 KB PRG ROM bank for CPU $8000-$FFFF
     ++--- Select 8 KB CHR ROM bank for PPU $0000-$1FFF

Hardware

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 /ROMSEL and R/W on its enable inputs, but /ROMSEL is 1 while M2 is low, not just while M2 is high and and A15 is low. 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]

See also: Oversize