SNROM

SNROM (NES-SNROM and HVC-SNROM) is a common board within the SxROM set. Like other SxROM boards, SNROM uses the Nintendo MMC1 ASIC.

Overview

• PRG ROM size: 128 or 256 KB
• PRG ROM bank size: 16 KB or 32 KB
• PRG RAM: 8 KB plus optional battery
• CHR capacity: 8 KB RAM
• CHR bank size: 8 KB or 4 KB
• Nametable mirroring: Controlled by mapper
• Subject to bus conflicts: No

Solder pad config

• PRG RAM retaining data : The pad below D2 (named 'SL' in recent revisions) disconected, and with Battery, D1, D2 and R2 present.
• PRG RAM not retaining data : Leave slots for Battery, D1, D2 and R2 free, and the pad below D2 (also named 'SL' in recent revisions) connected.

Banks

• CPU $6000-$7FFF: 8 KB PRG RAM bank, fixed
• CPU $8000-$BFFF: 16 KB PRG ROM bank, either switchable or fixed to the first bank
• CPU $C000-$FFFF: 16 KB PRG ROM bank, either fixed to the last bank or switchable
• PPU $0000-$0FFF: 4 KB switchable CHR RAM bank
• PPU $1000-$1FFF: 4 KB switchable CHR RAM bank

Chips and pinouts

• PRG ROM - 2 MBits (256 kB x 8) (DIP-32)

                 ---_---
          A17 - |01   32| - +5V
          /CE - |02   31| - +5V
          A15 - |03   30| - +5V
          A12 - |04   29| - A14
          A7  - |05   28| - A13
          A6  - |06   27| - A8 
          A5  - |07   26| - A9
          A4  - |08   25| - A11
          A3  - |09   24| - A16
          A2  - |10   23| - A10
          A1  - |11   22| - /CE
          A0  - |12   21| - D7
          D0  - |13   20| - D6
          D1  - |14   19| - D5
          D2  - |15   18| - D4
         GND  - |16   17| - D3
                 -------

PRG ROMs of 1 MBit (128 kB x 8) comes in a DIP-28 packages are sit 2 rows back (only pins 3 to 30 are used). This pinout is not compatible with stantard 27C020 EPROMs, nor with standard 27C010 EPROMs, so to insert them in the board manual rewiring is needed.

• CHR RAM - 64 KBits (8 KB x 8) : Standard 6264 pinout.

• PRG RAM - 64 KBits (8 KB x 8) : Standard 6264 pinout.

• MMC1 pinout

See also

• Nintendo MMC1