I've seen videos of it being done, but I can't seem to understand where the MIDI is being connected and how it works... Anyone know?
It's a normal ROM. The cartridge turns out to have also hardware to allow MIDI input. The program in the ROM just reads the port and controls the YM2612 as usual. Nothing weird to be honest.
Well, the MIDI device could have an adapted output port that can be used with one of the MD I/O ports. I was supposing the standard MIDI plug =P And I don't see any cartridge there at all o_O EDIT: that seems to be a modded MD so only the YM2612 is actually being used. Look at all the cables =S
I guess the guy is called Little-Scale who is doing the MD and MIDI stuff ? I need to contact him a bit to get more info... I'm doing similiar thing, though I'm not using MIDI...
from what I know, Little-Scale uses an arduino board http://en.wikipedia.org/wiki/Arduino to convert MIDI signals into data that can read via the controller port of the Mega Drive. He's got a flash cart in that picture, which is running custom software he wrote to interpret this data and set the FM registers accordingly. I don't doubt the authenticity of this since this guy has made heaps of of chip music related devices before.