The MIDI Drum Machine began in the Fall of 1991 as a project for a microprocessor system design course, shortly after I wrote PAULMON1, the 8051 monitor/debugger. A friend, Rod Seely, both a musician and electronics hobbiest suggested I design something using the Musical Instrument Device Interface, MIDI, that would be COOL and would work together with his collection of MIDI keyboards and synthesizers. Of course, I wanted to build something that could end up as a finished commercial product.
Source :http://www.pjrc.com/tech/midi-drums/drum-intro.html