Line-seizing circuitry is disclosed by which a plurality of remote terminals may be connected to a central data recorder over a single two-wire data line with only one terminal being in communication with the recorder at any one time. Tie-breaking circuitry is included to prevent two remote units from...http://www.google.es/patents/US4055835?utm_source=gb-gplus-sharePatente US4055835 - Line-seizing apparatus
