GENESIS2PCE

This adapter PCB allows connecting Genesis 3 or 6 button controllers to a PC Engine console. It consists of all the components a real PC Engine 6 button controller has + an Atmega328p for interfacing with Genesis controllers. When connecting a Genesis 6 button controller without holding the Mode button, the adapter will go into 6 button mode. This means you can use it as an actual 6 button PC Engine adapter for the handful of games that support it (Street Fighter 2, Art of Fighting, Fatal Fury 2 etc.). To ensure compatiblity with other games and the Sega Genesis 6 button controller, one should hold the Mode button while powering on the adapter to put the controller into 3 button mode and the adapter into 2 button mode. Sega Genesis 3 button controllers will always put the adapter into 2 button mode.

Which mode the adapter is currently in, is represented by the onboard LED.

LED on	LED off
6 button mode	2 button mode

File structure

Gerber files can be found in the Gerber directory
BOMs can be found in the BOM directory
Hex files for flashing the Atmega328p can be found in the Hex directory
Project source can be found in the GENESIS2PCE directory

Images

Mapping

PC Engine	Sega Genesis 3 button	Sega Genesis 6 button
Up	Up	Up
Down	Down	Down
Left	Left	Left
Right	Right	Right
Select	Start / A	Start / Mode
Run	A / Start	Mode / Start
I	C	C
II	B	B
III	--	A
IV	--	X
V	--	Y
VI	--	Z

The button assignments for Select and Run can be swapped. To do this, simply hold A, B, C & Start on your connected Genesis controller for 8 seconds. This configuration will be retained through power cycles.

Flashing the Atmega328p

The hex files for flashing the Atmega328p are available inside the Hex directory. The Atmega328p's fuse bytes should be set to the following values:

Fuse Byte	Value
Fuse Low Byte	0xDF
Fuse High Byte	0xFE
Extended Fuse Byte	0xFC

References

Very helpful information on how to read Genesis controllers was gathered from these sources: