Actually, the DMX signal itself is based off of an existing serial protocol, however it's RS422 (I think), not the RS232 we're used to seeing. If you're interested in learning about DMX as a control signal, as well as just about any other control system used in Entertainment, I suggest reading John Huntington's book, "Control Systems for Live Entertainment." He is one of my professors, and I have taken several of his classes. He is one of the foremost experts on Control systems and show control (they aren't the same!), and his book explores many different control types in Audio, Video, Scenery, etc, as well as lighting.