NINA-001

NINA-001 is a particular third-party cartridge board used by American Video Entertainment. The iNES format assigns mapper 34 to this board (as well as BxROM).

Overview

• PRG ROM size: 64 KB
• PRG ROM bank size: 32 KB
• PRG RAM: 8 KB, not battery backed [1]
• CHR ROM capacity: 32 KB ROM
• CHR bank size: 4 KB
• Nametable mirroring: hardwired to horizontal mirroring
• Subject to bus conflicts: No

Banks

• CPU $8000-$FFFF: 32 KB switchable PRG ROM bank
• PPU $0000-$0FFF: 4 KB switchable CHR ROM bank
• PPU $1000-$1FFF: 4 KB switchable CHR ROM bank

Registers

PRG bank select ($7FFD)

7  bit  0
---- ----
xxxx xxxP
        |
        +- Select 32 KB PRG ROM bank for CPU $8000-$FFFF

CHR bank select 0 ($7FFE)

7  bit  0
---- ----
xxxx CCCC
     ||||
     ++++- Select 4 KB CHR ROM bank for PPU $0000-$0FFF

CHR bank select 1 ($7FFF)

7  bit  0
---- ----
xxxx CCCC
     ||||
     ++++- Select 4 KB CHR ROM bank for PPU $1000-$1FFF

Hardware

The NINA-001 board contains a 74LS133 (13-input NAND gate), 74LS74 (dual D flip-flop), 74HCT139 (dual 1-4 decoder), 74LS00 (quad 2-input NAND gate), two 74HCT173s (4-bit tristate D flip-flop), as well as a microcontroller to act as a CIC defeat mechanism. These 4 registers reside "on top" of PRG RAM: each write to the register goes both to the register and to the RAM location at the same address. Thus, reading the register's address returns the last value written to the RAM, which is also the last value written to the register.

Variants

The iNES mapper used to implement this mapper also includes a writable register at $8000-$FFFF for emulation of the BxROM boardset (using CHR RAM instead of ROM, as well as lacking PRG RAM), which has caused many headaches for NES emulator authors. Emulator developers may consider switching between NINA-001 emulation and BxROM emulation based on the presence of CHR ROM.