NES 2.0 Mapper 357
NES 2.0 Mapper 357 is used for a 4-in-1 multicart (cartridge ID 4602) from Bit Corp. The first game is Bit Corp's hack of the YUNG-08 conversion of Super Mario Brothers 2 (J) named Mr. Mary 2, the other three games are UNROM games.
Unlike most multicarts, there is no menu; instead, the desired game is selected via two DIP Switches that protrude through the cartridge shell. The DIP switches directly select the outer 128 KiB PRG-ROM bank, game-specific nametable mirroring and mapper mode --- outer bank 0 selects SMB2J mode, all others select UNROM mode. All four games use 8 KiB of unbanked CHR-RAM. Mirroring is Vertical for banks 0-2 and Horizontal for bank 3.
Banks in SMB2J mode
- CPU $5000-$5FFF: 4 KiB PRG-ROM bank, fixed to #16
- CPU $6000-$7FFF: 8 KiB PRG-ROM bank, switchable to #2 or #0
- CPU $8000-$9FFF: 8 KiB PRG-ROM bank, fixed to #1
- CPU $A000-$BFFF: 8 KiB PRG-ROM bank, fixed to #0
- CPU $C000-$DFFF: 8 KiB PRG-ROM bank, switchable
- CPU $E000-$FFFF: 8 KiB PRG-ROM bank, switchable to #10 or #8
- PPU $0000-$1FFF: unbanked 8 KiB CHR-RAM
Registers in SMB2J mode
PRG Bank Select 1 ($4022, write)
Mask: probably $71FF
Bit 7654 3210
---------
.... .CCC
+++- Select 8 KiB PRG-ROM bank at CPU $C000-$DFFF.
The actual bank number is:
Value Bank# ------------ 0 4 1 3 2 5 3 3 4 6 5 3 6 7 7 3
PRG Bank Select 2 ($4120, write)
Mask: probably $71FF
Bit 7654 3210
---------
.... ...I
+- 0: CPU $6000-$7FFF to bank 2,
CPU $E000-$FFFF to bank 10
1: CPU $6000-$7FFF to bank 0,
CPU $E000-$FFFF to bank 8
IRQ Control ($4122)
Mask: probably $F1FF
Bit 7654 3210
---------
.... ...I
+- 0: Acknowledge and disable IRQ, reset counter
1: Enable IRQ
When enabled, the 12-bit IRQ counter increases on every M2 cycle until it overflows, upon which an IRQ is fired.
