INES Mapper 038

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