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: 2 or 4 KiB, not bankswitched, only in Family Basic (but most emulators provide 8)
- CHR capacity: 8 KiB ROM (DIP-28 standard pinout)
- CHR bank size: Not bankswitched, see Variants or see CNROM
- Nametable mirroring: Solder pads select vertical or horizontal mirroring
- Subject to bus conflicts: Yes, but irrelevant
Banks
All Banks are fixed,
- CPU $6000-$7FFF: Family Basic only: PRG RAM, mirrored as necessary to fill entire 8 KiB window, write protectable with an external switch
- 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. RTROM and STROM split PRG into two 8KiB ROMs. 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 KiB WRAM (or 4 KiB WRAM for v3) accessible at $6000-$7FFF and decoded with a 74HC20, that is backed with 2 AA batteries. The cartridge is equipped with a back up switch that, when enabled, write-protects WRAM to prevent possible data corruption if the Famicom is turned on or off.
Disch's Notes
Here are Disch's original notes: ======================== = Mapper 000 = ======================== aka -------------------------- NROM "no mapper" Example Games: -------------------------- Ice Climber (J) (RROM) Excitebike Balloon Fight Super Mario Bros. Notes: -------------------------- No swapping of any kind. All slots fixed, mirroring is hardwired, etc.
