MHROM

NES-MHROM is a board of the GxROM family cartridge boards.

Overview

• PRG ROM size: 64 KB
• PRG ROM bank size: 32 KB
• PRG RAM: None
• CHR capacity: 8 KB, 16 KB or 32 KB ROM
• CHR bank size: 8 KB
• Nametable mirroring: Solder pads select vertical or horizontal mirroring
• Subject to bus conflicts: Yes

Banks

• CPU $8000-$FFFF: 32 KB switchable PRG ROM bank
• PPU $0000-$1FFF: 8 KB switchable CHR ROM bank

The MHROM board always have 2 PRG ROM banks, and 1, 2 or 4 CHR ROM banks.

Solder pad config

• Horizontal mirroring : 'H' disconnected, 'V' connected.
• Vertical mirroring : 'H' connected, 'V' disconnected.

Chips and pinouts

• PRG ROM - 512 kBit (64 KB x 8) (DIP-28)

              ---_---
       A15 - |01   28| - +5V
       A12 - |02   27| - A14
       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| - GND (/CE ?)
       A0  - |10   19| - D7
       D0  - |11   18| - D6
       D1  - |12   17| - D5
       D2  - |13   16| - D4
       GND - |14   15| - D3
              -------

This pinout is compatible with standard 27C512 EPROMs, no rewiring needed.

• CHR ROM - 256 kBit (32 KB x 8) (DIP-28)

              ---_---
       +5V - |01   28| - +5V
       A12 - |02   27| - A14
       A7  - |03   26| - A13
       A6  - |04   25| - A8
       A5  - |05   24| - A9
       A4  - |06   23| - A11
       A3  - |07   22| - /OE (/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
              -------

This pinout is compatible with standard 27C256 EPROMs, as well with 27C128 (16 KB) and 27C64 (8 KB). No rewiring is needed at all.