Video URL: http://www.youtube.com/watch?v=-STfPfXQcps
A device that electronically manipulates the controller port pins of the Sega Master System so that the console detects presses and depresses of buttons based on MIDI note events. Both controller ports are supported.
When the device receives a MIDI note on message at a particular pitch, it switches that particular button on. When the device receives a MIDI note off message at a particular pitch, it switches that particular button off.
Gameplay sequences can be controlled and playedback from a PC to the Master System in this fashion.
I am sure we all realise what the next step is in this project.