A switchable termination module for use with addressable devices on a communication bus has a terminator for each signal transmission path, a signal source, for example a switch for signalling whether termination is desired and a terminator control circuit for engaging and disengaging the terminators...http://www.google.de/patents/US4920339?utm_source=gb-gplus-sharePatent US4920339 - Switchable bus termination and address selector
