GenMDM is a MIDI interface for the Sega Mega Drive / Genesis allowing full control of the 6 channels of the Yamaha YM2612 FM synthesis chip and the 4 channels of the PSG SN76489 chip that are inside your Sega Mega Drive / Genesis.

Sadly, the original GenMDM by little-scale is no longer available for purchase. This project recreates the GenMDM interface for the Sega Mega Drive / Genesis using a Teensy 2.0 and a 3.5mm TRS MIDI in jack.

View the GenMDM Assembly and Ordering Guide [docs.google.com]

Digikey parts list:

https://www.digikey.com/en/mylists/list/6386959T7V (all parts but the Teensy 2.0)

Mouser parts list (alternate):

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=08d240b967 (all parts but the 3.5mm jack, and the Teensy 2.0)

This requires a Teensy 2.0 programmed with the little-scale GenMDM firmware and the GenMDM cartridge for the Sega Genesis.

GenMDM firmware [web.archive.org] for Teensy 2.0 by little scale

GenMDM cartridge file [web.archive.org] for Sega Megadrive / Genesis flash cart

BEWARE OF FAKE TEENSYS!!  

https://www.pjrc.com/teensy/counterfeit.html 

Fake Teensy 2.0's are abundant. The four I bought off ebay did not ship with a bootloader. You will need an ISP programmer to upload the GenMDM firmware to a fake Teensy instead of being able to program it with the Teensy Loader application over the USB port. Because of this, I can only recommend the use of genuine PJRC Teensy 2.0's which are hard to find. I was able to get a genuine PJRC Teensy 2.0 in 2024 from 1Up Keyboards https://1upkeyboards.com/shop/parts-and-tools/pjrc-teensy-2-0/ 

If you already know how to program an MCU with an ISP programmer, then a fake Teensy will work in the GenMDM.

How to use the jumper:

• When the jumper is closed, the Teensy 2.0 and MIDI input circuit are powered by the 5 volts provided on the SEGA Genesis controller port.
• When the jumper is removed, no power is taken from the SEGA Genesis console. The Teensy 2.0 and MIDI in circuit will need to be powered through the USB port on the Teensy 2.0.
• Always remove the jumper when using the USB port on the Teensy 2.0 while the GenMDM is plugged into the Sega Megadrive / Genesis. FAILURE TO REMOVE THE JUMPER WHEN USING USB MAY CAUSE DAMAGE TO THE TEENSY, SEGA CONSOLE, OR YOUR COMPUTER/POWER SUPPLY. 

USE THE GENMDM AT YOUR OWN RISK

The 3.5mm (1/8 inch) MIDI input is wired for Type A MIDI cables.

• Type A MIDI Cable (male 5-pin to 3.5mm TRS) https://www.amazon.com/dp/B0D96B15BF
• Type A MIDI Cable (female 5-pin to 3.5mm TRS) https://www.amazon.com/dp/B0C2RLB3SL

For more information on the GenMDM by little-scale, see https://chipmusic.org/forums/post/8135/