FamicomBox+ Mod Overview
FamicomBox+ Mod Overview
The FamicomBox+ mod was designed to address several of the original Famicom Box's hardware flaws. The standard Famicom Box can switch between up to 16 cartridges, but its design shares certain pins across all slots (including IRQ, M2, and PPU /RD), which can lead to compatibility and performance issues. The FamicomBox+ mod resolves these problems with a range of hardware improvements.
Key Features and Improvements
- Demultiplexes M2 (Pin 38) to all 16 cartridges
- Multiplexes /IRQ (Pin 15) from all 16 cartridges
- Multiplexes CIRAM /CE (Pin 57) from all 16 cartridges
- Demultiplexes PPU A12 (Pin 64) to all 16 cartridges
- Demultiplexes PPU /RD (Pin 21) to all 16 cartridges
- Supplies PPU /A13 (Pin 58) to all cartridges
- Isolates EXP0, EXP1, EXP2, EXP3, EXP4, EXP5, EXP7, EXP8, and EXP9
- Allows two cartridges to use EXP6 for expansion audio, including volume control
- Fixes open bus issues on certain games (e.g., Paper Boy)
- Disables the second RAM chip ($6000-$7FFF) when in-game, enabling proper SRAM and related functions
- Enables or disables $5xxx when in-game (used by some games and the Everdrive)
⚠️ Important Famicom Box Warning
On a stock Famicom Box, the EXP lines are connected directly to either 5V or GND depending on the slot, which is used for CIC addressing. However, some cartridges use these ports for debugging or audio. If you use a stock Famicom Box, you may damage certain cartridges when plugging them in.
Limitations
- This mod is complex to install and requires experience with de-soldering ICs, soldering mod wires, and troubleshooting hardware.
- It may not work with modern games that require tighter timing, or with bootleg cartridges (e.g., from AliExpress).
Tested Games
The following games have been tested and confirmed working with the FamicomBox+ mod:
- Castlevania 3 (Famicom, with expansion audio)
- The Legend of Zelda
- The Adventure of Link
- Super Mario Bros
- Super Mario Bros 2
- Super Mario Bros 3
- Gauntlet II
- Tetris
- Snake Rattle N Roll
- The Little Mermaid
- Excitebike
- Tennis
- Duck Hunt
- Wrecking Crew
- Captain Planet and the Planeteers
- High Speed
- Yoshi
The Famicom Disk System RAM adapter also fits in Slot 14, and the mod works with Everdrive cartridges.
Note: Some games may still not work due to timing issues. Only the above titles have been fully tested—compatibility with other games is not guaranteed.
Menu System
The original menu checks an internal game database or looks for the Nintendo header in each ROM. Most games lack the correct header or database entry, so they're rejected by default.
Our custom menu modification allows any game to appear in the menu, though they’ll be displayed simply as "NES GAME" instead of showing the actual game name.
Special Thanks
Huge thanks to Lidnariq for sharing his knowledge and guidance—his insights into the differences between the Famicom Box and the modded board were invaluable.
Additional thanks to Fiskbit, who helped reverse-engineer and enhance the menu software, enabling more games to run and improving console boot-up times.