INES Mapper 153

iNES Mapper 153 is used for a Bandai FCG board with an LZ93D50 ASIC and 8192 bytes of battery-backed WRAM. These 8192 bytes must be denoted as PRG-NVRAM in the NES 2.0 header using byte value $70. Only one game, Famicom Jump II: Saikyou no 7-nin, uses this mapper.

Banks

• CPU $6000-$7FFF: 8 KiB battery-backed WRAM
• CPU $8000-$BFFF: 16 KiB switchable PRG-ROM bank
• CPU $C000-$FFFF: 16 KiB PRG ROM bank, fixed to the last bank
• PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM

Registers

Outer PRG-ROM Bank Select ($8000-$8003 write)

Mask: $800F

7  bit  0
---- ----
xxxx xxxP
        |
        +-- Select 256 KiB outer PRG-ROM bank at CPU $8000-$FFFF

• The same value must be written to all four registers, or the outer PRG-ROM bank would be switched as the PPU is rendering.
• Because the ASIC's PA12 and PA13 inputs are grounded, only registers $8000-$8003 instead of $8000-$8007 are relevant.
• No CHR banking is available.

Inner PRG-ROM Bank Select ($8008 write)

Mask: $800F

7  bit  0
---- ----
.... PPPP
     ||||
     ++++-- Select 16 KiB inner PRG-ROM bank at CPU $8000-$BFFF   

Nametable Mirroring Type Select ($8009 write)

Mask: $800F

7  bit  0
---- ----
.... ..MM
       ||
       ++-- Select nametable mirroring type
             0: Vertical
             1: Horizontal
             2: One-screen, page 0
             3: One-screen, page 1

IRQ Control ($800A write)

Mask: $800F

7  bit  0
---- ----
.... ...C
        |
        +-- IRQ counter control
             0: Counting disabled
             1: Counting enabled

• Writing to this register acknowledges a pending IRQ, and copies the latch to the actual counter.
• If a write to this register enables counting while the counter is holding a value of zero, an IRQ is generated immediately.

IRQ Latch/Counter ($800B-$800C write)

Mask: $800F

   $C         $B
7  bit  0  7  bit  0
---- ----  ---- ----
CCCC CCCC  CCCC CCCC
|||| ||||  |||| ||||
++++-++++--++++-++++-- Counter value (little-endian)

• If counting is enabled, the counter decreases on every M2 cycle. When it holds a value of zero, an IRQ is generated.
• These registers modify a latch that will only be copied to the actual counter when register $xxxA is written to.

PRG-RAM Control ($800D write)

Mask: $800F

7  bit  0
---- ----
..E. ....
  |
  +-------- PRG-RAM Chip Enable (1=Enable)

Note

When booting with WRAM filled with zeroes, Famicom Jump II will freeze with a black screen. Simply soft-resetting the console will then always run the game properly unless WRAM is zeroed out again.