Communication system having stations capable of detecting another station's

A communication system having a connecting line and stations connected thereto for transmitting and receiving information, each station comprising a processor, a transmitting stage and a receiving stage, the processor in each station having free access to the connecting line via the transmitting stage, and each station including a detector for switching off the transmitting station upon detection of the presence of another station requesting and having, respectively, substantially simultaneous access to the connecting line, characterized in that at a station which requests or has access to the connecting line in which station the transmitting stage and the receiving stage are both connected to the connecting line, an output impedance of the transmitting stage, when it supplies a predetermined logic value, is temporarily increased by impedance increasing means to at least the order of magnitude of the characteristic impedance of the connecting line, the detector, which is coupled to an output of the receiving stage, producing a detection signal which switches off the transmitting station when, during the increase in impedance, the receiving stage receives a logic value which is different from said predetermined logic value.