Transmitters and receivers for controlling remote elements which use a synchronous serial transmission format and which allows changes in coding to be automatically made between the receiver and transmitter and wherein the code is stored in memories of the transmitter and receiver and wherein the receiver...http://www.google.com.au/patents/US4529980?utm_source=gb-gplus-sharePatent US4529980 - Transmitter and receiver for controlling the coding in a transmitter and receiver
