A data transmission system is described where data signals are bidirectionally transmitted between a data transmitter and a plurality of data receivers in a self-clocking bit streams carried on true data and complement data signal lines and a non-return-to-zero (NRZ) bit streams on a return data signal...http://www.google.es/patents/US4369516?utm_source=gb-gplus-sharePatente US4369516 - Self-clocking data transmission system
