If you want to play games on your Genesis/Megadrive console but have a strong preference for SNES controllers, or own many cool arcade sticks for the SNES which you'd like to use, an adapter to connect SNES controllers to your Genesis/Megadrive is exactly what you need.

I used an Atmel atmega8a MCU do build this adapter, and optimising the code until it would react fast enough to the console requests was a fun challenge which I took the time to document.



See also: SNES controller to Atari/Commodore adapter

Genesis	SNES 1	SNES 2	SNES 3	SNES 4	SNES 5
Start	Start	Start	Start	Start	Start
Mode	Select	Select	Select	Select	Select
A	A	B	Y	X	A
B	B	A	B	Y	B
C	X	Y	A	B	X
X	Y	X	L	A	Y
Y	L	L	X	R	L
Z	R	R	R	L	R
D-Up	D-Up	D-Up	D-Up	D-Up	D-Down
D-down	D-down	D-down	D-down	D-down	D-up
D-left	D-left	D-left	D-left	D-left	D-right
D-right	D-right	D-right	D-right	D-right	D-left

Enabling a mapping:
Mappings are enabled by holding buttons on the SNES controller when connecting the adapter or turning the console on.

Mapping	Activation
SNES 1	Default
SNES 2	Hold B
SNES 3	Hold Y
SNES 4	Hold X
SNES 5	Hold L

I used a simplified version of my multiuse pcb2 for this project. The only components present are the microcontroller, capacitors, and a 16 MHz crystal.

Schematic:

Wiring:

Wiring tables for the Genesis/Megadrive (DB9-F connector) and SNES controller:

DB9 Pin	Signal name	AVR pin name
1	UP/UP/Z	PC5
2	DN/DN/Y	PC4
3	0/LF/X	PC3
4	0/RT/	PC2
5	VCC	VCC
6	A/B	PC1
7	SELECT	PD2 (INT0)
8	GND	GND
9	START/C	PC0

SNES pin	AVR pin name
VCC	VCC
GND	GND
CLOCK	PB5
DATA	PB4
LATCH	PB3

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Here are a few pictures of my development setup, all wired according to the above tables. Notice how the standard solder cup DB9-F I used to connect to the console cannot be fully inserted. Ideally a Genesis/Megadrive controller or extension cable should be used.

Version v1.5.1 October 22, 2016 (Saturday)
Atmega168 support
File(s): snes2md-1.5.1.tar.gz (21.3 KB) snes2md.m168.1.5.1.hex (6 KB) snes2md.m8.1.5.1.hex (5.8 KB)

Version v1.4 July 26, 2014 (Saturday)
The adapter is now usable with SMS games running on a Megadrive/Genesis
File(s): snes2md-1.4.tar.gz (20.6 KB) snes2md-1.4.hex (5.8 KB)

Version v1.3 June 23, 2014 (Monday)
Add a 3 button compatibility mode. Hold SELECT at power up to enable.
File(s): snes2md-1.3.tar.gz (20.5 KB) snes2md-1.3.hex (5.4 KB)

Version v1.2 October 29, 2013 (Tuesday)
New features: Added two new Genesis mappings Added a new Atari mapping Added support for 2nd fire button (Amiga) Added auto-fire for Atari mode (Button 1/Fire). Selectable auto-fire speed 30Hz, 25Hz, 20Hz, 16.667Hz, 15Hz and 12.5Hz Auto-fire lock mode for Button 1/Fire. (Toggled by START)
File(s): snes2md-1.2.tar.gz (19.8 KB) snes2md-1.2.hex (5.3 KB)

Version v1.1.1 October 20, 2013 (Sunday)
Updated Atari mode mappings.
File(s): snes2md-1.1.1.tar.gz (18.7 KB) snes2md-1.1.1.hex (3.4 KB)

Version v1.1 October 8, 2013 (Tuesday)
Implemented Atari/Commodore support: Two selectable button mappings Enabled by grounding PB1. Note: A slightly different DB9 wiring is required.
File(s): snes2md-1.1.tar.gz (18.6 KB) snes2md-1.1.hex (3.4 KB)

Version v1.0 September 14, 2013 (Saturday)
Initial release: Genesis/Megadrive 6 button pad emulation 3 Selectable button mappings
File(s): snes2md-1.0.tar.gz (18.1 KB) snes2md-1.0.hex (2.8 KB)

Using the .hex files

The micro-controller (Atmega8 or Atmega168) needs to be programmed with the correct .hex file. The "fuse bytes" for this project are:

• Atmega8: high_byte=0xc9, low_byte=0x9f.
• Atmega168: high_byte=0xdc, low_byte=0xd7, extended_byte=0x01

For more information about the tools required to program an AVR microcontroller, please visit my AVR programming page.

Source Code (.tar.gz files):
Unless indicated otherwise, the source code is published under the GPL license. Please consult the included LICENSE file for more information. The project compiles using the included makefiles using avr-gcc under Linux.

I like seeing how others build my projects. If you build an adapter, please send me pictures and I'll add them here.

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January 6, 2015 (Tuesday)
Roman Sysoev from Russia sent me the following pictures of the prototype and final PCB version (enclosure still missing) of the SNES controller to Genesis/Megadrive he built.

The following document(s) were useful:

• Sega Six Button Controller Hardware Info

I cannot be held responsible for any damages that could occur to you or your equipment while following the procedures present on this page. Also, I GIVE ABSOLUTELY NO WARRANTY on the correctness and usability of the informations on this page. Please note, however, that the procedures above have worked in my case without any damages or problems.

Now you cannot say that I did not warn you :)