Circuit arrangement for connecting a subscriber to a bus line via switch means under which prevents disabling of the bus line in the event of driver failure

Claim 1

A circuit arrangement for coupling a subscriber device to a bus line comprising transmitter means coupled between the subscriber device and the bus line, the transmitter means being coupled in a low impedance state to the bus line upon receipt of a first signal from the subscriber device and in a high impedance state in the absence of said signal, the circuit arrangement further comprising electronic switch means comprising a switching path and a control input, the switching path being switched into conduction if said first signal is received at said control input, said switching path of said switch means being coupled between said transmitter means and said bus line, a plurality of connecting lines between the transmitter means and the electronic switch means being provided, the connecting lines each being coupled via a resistor to a constant potential source, and further comprising logic means coupled to the connecting lines for providing a fault signal in the event of different potentials on the connecting lines, said logic means providing said fault signal in the event at least one of said switch means short circuits, whereby a selected logic signal from said bus line on at least one of said connecting lines due to said short circuited switch means will be coupled to said logic means thereby to generate said fault signal.