Genesis Reproduction Board Guide

Here’s a quick guide on how to populate my custom designed Genesis/Mega Drive reproduction PCBs. It supports most Genesis games.

Front Side

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EPROM

Needed for: Every game
Part Number: 27C322 or 27C160 (remember to kick out pin 32 on the 27C160 if using it)
Function: Holds the ROM file
How to Program: Use an EPROM programmer and load the ROM file; be sure it is byte-swapped before programming.

C1 – Electrolytic Capacitor

Needed for: Every game
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 – Ceramic Capacitor

Needed for: Every game
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the EPROM

C3, C4, C5 – Ceramic Capacitors

Needed for: Games that save
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the SRAM, Flip-Flop, and Decoder

R1, RC, RB – Resistors

Needed for: Games that save
Value: ~1 kΩ for R1 and RC, ~10 kΩ for RB
Function: Part of the battery management and saving logic circuit

D1, D2 – Diodes

Needed for: Games that save
Part Number: Any schottky diode will do, I used 1N914
Function: Combines battery and main power supply to power the SRAM

Q1 – NPN Transistor

Needed for: Games that save
Part Number: 2N2222 or equivalent
Function: Part of the battery management and saving logic circuit

74HC74 – D-type Flip-Flop

Needed for: Games that save, for ROM files that are larger than 16 Mbit
Part Number: 74HC74 or equivalent
Function: Part of the saving logic circuit

74HC139 – Decoder

Needed for: Games that save
Part Number: 74HC139 or equivalent
Function: Switches between activating the ROM or the RAM during gameplay

SRAM

Needed for: Games that save
Part Number: 62256 series SRAM (be sure to get low standby current model)
Function: Holds save game data

Battery

Needed for: Games that save
Part Number: C2032 (socket is designed for yellow ones with pre-attached legs)
Function: Keeps the SRAM on to retain data while power is off

Solder Pads

If your game does not save: Bridge the solder pad on the right of the 74HC139 package
If your game saves: Bridge the solder pad in the right hand corner

Back Side

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Solder Pads

EPROM selection: Bridge the pads in the middle of the board based on which EPROM you are using
ROM size selection: Bridge the middle pad to the left for games 16 Mbit or less, to the right for games larger than 16 Mbit (this is only necessary for games that save). Solder based on the original ROM size – if you expand a 16 Mbit game to 32 Mbits, for example, you should still use the “16 Mbit or less” solder pad.

Preparing the ROM

When programming Genesis games, you need to make sure you byte swap the ROM file before you program it. For this, I use the GQ-4×4 programming software – you don’t need to have a GQ-4×4 to use this software! You could just use it to byte swap your ROM and then save it to use a different programmer. To byte swap, just load up your ROM in the software, and click the “A<>B” button.

byteswap1

You can then save the ROM to use in another programmer, or go ahead and program with your GQ-4×4.

Important rework for older board revisions!

Needed for: Games that save, that have ROM files 16 Mbit or smaller
Rework: Solder pins 2 and 3 together on the 74HC139. Make sure the 74HC74 is not installed on the board.

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Examples of Completed Boards

If your game doesn’t save, it’s very easy to finish. You only need the electrolytic capacitor, one ceramic capacitor, and the EPROM.

If your game uses save data, you’ll need to populate every component, as shown here.

2 thoughts on “Genesis Reproduction Board Guide

    • No men, instead support this guy buying some of the boards on his store, he made all this guides for free and even answer your questions on facebook.

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