NES 2.0 Mapper 264

NES 2.0 Mapper 264 is used for two fighting games from Yoko Soft (aka Cony):

• Mortal Kombat II/V Pro
• Master Fighter VI'

It is similar but not quite identical to several other Cony mappers. Its UNIF board name is UNL-YOKO.

Registers

DIP switch(read)

Mask: Probably $D400

$5000: Bit 7654 3210
           ---------
           .... ..DD
                  ++- DIP switch value

Scratch RAM (read/write)

Mask: Probably $D403

$5400: Scratch RAM byte #0
$5401: Scratch RAM byte #1
$5402: Scratch RAM byte #2
$5403: Scratch RAM byte #3

Outer PRG-ROM Bank ($8000)

Mask: Probably $8C17

7654 3210
---------
.... OPPp
     |||+- Select 16 KiB PRG-ROM bank at CPU $8000-$FFFF in PRG banking mode 0
     |++-- Select 32 KiB PRG-ROM bank at CPU $8000-$FFFF in PRG banking modes 0 and 1
     +---- Select 128 KiB PRG-ROM bank at CPU $8000-$FFFF in all PRG banking modes

Mode ($8400)

Mask: Probably $8C17

7654 3210
---------
ID.B B.MM
|| | | ++- Select nametable mirroring
|| | |      0: Vertical
|| | |      1: Horizontal
|| | |      2: One screen, page 0
|| | |      3: One screen, page 1
|| +-+---- Select PRG banking mode
||          0: 16 KiB UNROM-like:
||             CPU $8000-$BFFF: 16 KiB PRG-ROM bank selected by Outer Bank register ($8000)
||             CPU $C000-$FFFF: 16 KiB PRG-ROM bank fixed to last bank (UNROM-like)
||          1: 32 KiB:
||             CPU $8000-$FFFF: 32 KiB PRG-ROM bank selected by Outer Bank register ($8000) SHR 1
||          2: 8 KiB:
||             CPU $8000-$9FFF: 8 KiB PRG-ROM bank selected by Inner PRG-ROM Bank register 0 ($8C00)
||                              and Outer Bank register bit 3 SHL 1
||             CPU $A000-$BFFF: 8 KiB PRG-ROM bank selected by Inner PRG-ROM Bank register 1 ($8C01)
||                              and Outer Bank register bit 3 SHL 1
||             CPU $C000-$DFFF: 8 KiB PRG-ROM bank selected by Inner PRG-ROM Bank register 2 ($8C02)
||                              and Outer Bank register bit 3 SHL 1
||             CPU $E000-$FFFF: 8 KiB PRG-ROM bank selected by Inner PRG-ROM Bank register 3 ($8C03)
||                              and Outer Bank register bit 3 SHL 1
||          3: Same as 2.
|+--------- IRQ counting mode
|            0: Increase
|            1: Decrease
+---------- IRQ Enable latch

IRQ Acknowledge and Counter Low ($8800)

A write directly changes the low eight bits of the 16-bit IRQ counter and acknowledges the IRQ.

Mask: Probably $8C17

IRQ Enable and Counter High ($8801)

A write directly changes the high eight bits of the 16-bit IRQ counter, and copies bit 7 of the Mode register to the actual IRQ Enable register (which is not directly accessible).

Mask: Probably $8C17

Inner PRG-ROM Bank ($8C0x)

These registers only have an effect in 8 KiB PRG-ROM banking mode (see $8400 bits 3 and 4). They are ORed with bit 8 SHL 1 of the Outer PRG-ROM bank register ($8000).

Mask: Probably $8C17

7654 3210
---------
.... PPPP
     ++++- Set Inner 8 KiB PRG-ROM bank

8C00: Set Inner 8 KiB PRG-ROM bank at CPU $8000-$9FFF
8C01: Set Inner 8 KiB PRG-ROM bank at CPU $A000-$BFFF
8C02: Set Inner 8 KiB PRG-ROM bank at CPU $C000-$DFFF
8C03: Set Inner 8 KiB PRG-ROM bank at CPU $E000-$FFFF

2 KiB CHR-ROM Banks ($8C1x)

Mask: Probably $8C17

8C10: Set 2 KiB CHR-ROM bank at PPU $0000-$07FF
8C11: Set 2 KiB CHR-ROM bank at PPU $0800-$0FFF
8C16: Set 2 KiB CHR-ROM bank at PPU $1000-$17FF
8C17: Set 2 KiB CHR-ROM bank at PPU $1800-$1FFF

IRQ Operation

If the IRQ counter is enabled (by writing a value to $8801 after setting bit 7 in the Mode register), and the counter is not zero, the counter is increased (Mode register bit 6 clear) or decreased (Mode register bit 6 set) on every M2 cycle. If it reaches zero, an IRQ is raised, and the IRQ counter is automatically disabled.

Notes

• Although the DIP switch has two bits (the value read is ANDed with $03), both games only check whether it is zero/nonzero.
• Master Fighter VI' used the value read from DIP switch ($5200) to determine if game should be run in NTSC/Dendy (lowest bit equals 1) or PAL (lowest bit equals 0) mode
• Power-up state is unknown, but game Master Fighter VI' executes from $E000 and first what it does is to change mode to 2 and continues to execute code from the same place. So either power-up mode is 0/2/3 plus $8C03 needs to be set to $0F (or maybe every bit of every register is initialized with ones)