NROM
The generic designation NROM refers to the Nintendo cartridge boards NES-NROM-128, NES-NROM-256, their HVC counterparts, and clone boards. The iNES format assigns mapper 0 to NROM.
Overview
- PRG ROM size: 16 KiB for NROM-128, 32 KiB for NROM-256 (DIP-28 standard pinout)
- PRG ROM bank size: Not bankswitched
- PRG RAM: 8 KB, Not Bankswitched, Only in Family Basic
- CHR capacity: 8 KB ROM (DIP-28 standard pinout), or 8KB RAM in Family Basic
- CHR bank size: Not bankswitched, see Variants or see CNROM
- Nametable mirroring: Solder pads select vertical or horizontal mirroring
- Subject to bus conflicts: Yes
Banks
All Banks are fixed,
- CPU $8000-$BFFF: First 16 KB of ROM.
- CPU $C000-$FFFF: Last 16 KB of ROM (NROM-256) or mirror of $8000-$BFFF (NROM-128).
Solder pad config
- Horizontal mirroring : 'H' disconnected, 'V' connected.
- Vertical mirroring : 'H' connected, 'V' disconnected.
Registers
None. This has normally no mapping capability whatsoever!
Hardware
PRG ROM 256 kBit (32 KB x 8) (DIP-28) :
---_---
+5V - |01 28| - +5V
A12 - |02 27| - A14 (VCC on NROM-128)
A7 - |03 26| - A13
A6 - |04 25| - A8
A5 - |05 24| - A9
A4 - |06 23| - A11
A3 - |07 22| - /OE (/ROMSEL)
A2 - |08 21| - A10
A1 - |09 20| - /CE (GND)
A0 - |10 19| - D7
D0 - |11 18| - D6
D1 - |12 17| - D5
D2 - |13 16| - D4
GND - |14 15| - D3
-------
CHR ROM 64 kBit (8 KB x 8) (DIP-28) :
---_---
+5V - |01 28| - +5V
A12 - |02 27| - VCC
A7 - |03 26| - NC
A6 - |04 25| - A8
A5 - |05 24| - A9
A4 - |06 23| - A11
A3 - |07 22| - /OE (CHR /RD)
A2 - |08 21| - A10
A1 - |09 20| - /CE (CHR A13)
A0 - |10 19| - D7
D0 - |11 18| - D6
D1 - |12 17| - D5
D2 - |13 16| - D4
GND - |14 15| - D3
-------
EPROM Modifications
No modifications nessesary.
Variants
RROM and SROM are NROM with different CHR ROM pinouts, probably named for the Ricoh and Sharp ROMs used. HROM is an early NROM variant without the solder pads to select mirroring, only vertical mirroring available (as if the 'H' pad were selected).
NROM operates identically to a CNROM with one CHR bank, or BNROM with CHR ROM and only 32 KB PRG ROM.
Family Basic, released by Nintendo, Sharp, and Hudson, contains 2 to 4 KB WRAM (depending on version) accessible at $6000-$7FFF and decoded with a 74HC20, that is (wholy or partially?) backed with 2 AA batteries. The cartridge is equipped with a back up switch that, when enabled, write-protects WRAM area $6000-$6FFF to prevent possible data corruption if the Famicom is turned on or off.
