NES Reproduction Board Guide – MMC3

Please look at the main entry for more information on how to prepare the ROM file!

Here’s a guide on how to populate my custom designed NES reproduction PCB. This board supports most MMC3 games with the TxROM board name (where the lowercase ‘x’ is a stand-in for other board types). This means you can make games that use boards like TLROM, TGROM, etc. Check out the Nesdev wiki entry on TxROM games here. The board utilizes the AX5202 to imitate the MMC3 mapper.

Here is a table of the various TxROM boards and their required hardware. Note that a few board types are not supported: TQROM, TR1ROM, and TVROM.

Front Side

PRG ROM

Needed for: All game types
Part Number: EPROMs: 27C010, 27C020, 27C040, 27C080; Flash memory: 39SF010, 39SF020, 39SF040
Function: Holds the Program ROM file. This is placed in the socket marked PRG.
How to Program: Check the reproduction article for information (Steps 1, 3, and 4)

CHR ROM

Needed for: Most TxROM games, notably TLROM – check your board type using FamiROM
Part Number: EPROMs: 27C010, 27C020, 27C040, 27C080; Flash memory: 39SF010, 39SF020, 39SF040
Function: Holds the Character ROM file (sprite data). This is placed in the socket marked CHR.
How to Program: Check the reproduction article for information (Steps 1, 3, and 4)

CHR SRAM

Needed for: Some TxROM games – check your board type using FamiROM
Part Number: 6264 series
Function: Holds the ROM’s sprite data. This is placed in the socket marked CHR.

PRG RAM (WRAM)

Needed for: Some TxROM games – check your board type using FamiROM
Part Number: 6264 series
Function: Used for normal operation of some games, and/or holds save data. This is placed in the socket marked WRAM.

CIC

Needed for: All game types (unless using a top-loader NES, modded NES, or clone console)
Part Number: Original CIC, or programmed ATTiny13
Function: Completes the region check and allows the game to run on the console.

MMC3 – Mapper

Needed for: All games
Part Number: AX5202
Function: Used by the NES for memory management, allowing for increased memory size and features. Note that the AX5202 is not the original MMC3 chip, it is a clone chip that acts as a replacement for the MMC3 which is a proprietary chip designed by Nintendo. Many sources of AX5202 chips have been known to provide faulty parts from time to time, however any that I provide for purchase have been tested.

R1, D1, D2 – Resistor and Diodes

Needed for: Games that save
Value: ~1kΩ for R1, ~10kΩ for R2 and R3, Schottky diodes (such as 1N914 or BAT85) for D1 and D2
Function: R1 acts as a current limiting resistor from the battery supply to the RAM chip that holds save data. R2 and R3 are pull-down resistors for two pins on the mapper. Diodes combine the voltage from the NES and the voltage from the backup battery to power the RAM.

C1 – Electrolytic Capacitor

Needed for: All game types
Value: ~22 uF, at least 10 V rated
Function: Smooths out supply voltage for the board due to transients on the power supply, prevents quick changes in supply voltage when power is turned off.

C2, C3, C4, C5 – Ceramic Capacitors

Needed for: All game types
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the EPROMs, RAM, AX5202, and importantly, the CIC. There are two places for C2, depending on the CIC you are using – you only need to use the one closest to the chip you use.

C6 – Ceramic Capacitor

Needed for: Games that have PRG RAM (WRAM)
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the RAM chip.

C7 – Electrolytic Capacitor

Needed for: Games that save
Value: ~22 uF, at least 10 V rated
Function: 
Smooths out supply voltage for the board due to transients on the power supply, prevents quick changes in supply voltage when power is turned off. This is a contingency for preventing loss of save data.

CR2032 – Battery

Needed for: Games that hold save data
Value: CR2032 (socket is designed for yellow ones with pre-attached legs)
Function: 
Keeps the WRAM powered on after the NES is powered off to hold save data.

Back Side

CHR ROM/RAM Solder Pads

Solder the middle pads to either the left or right pads for either CHR ROM or CHR RAM, depending on your game.

Battery Bypass Solder Pad

This solder pad bypasses D2 for games that don’t hold save data, but use PRG RAM. Only solder this if you are using WRAM without a back-up battery. If you solder this with a battery on the board, it will drain the battery power quickly.

TxSROM Solder Pads

If your game is TKSROM or TLSROM, then solder the two middle pads to the bottom, indicated by “TxSROM”. If the game is any other board type, solder the two middle pads to the top, indicated by “OTHERS”.

You must solder these pads in one direction or the other for your game to operate. Obviously, most games you will be soldering to the “OTHERS” pad.

Flash/EPROM Solder Pads

Solder the middle pads to the left if using Flash memory (39SF series). Solder to the right if using UV EPROMs (27C series).

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