Abstract: In a plural channel safety output circuits, for example for railway safety purposes, binary signals of a pair of data lines are fed to two trigger elements each of which control a respective gate stage. These two gate stages receive clock pulses from a clock pulse generator which provide control for the entire data processing system. The signals emitted from the gate stages are monitored by a common equivalence monitoring element such that when the signal pairs at the outputs of the two gate stages are alike, the equivalence monitoring element passes test pulses released by the clock pulse generator back to the clock pulse generator to maintain the clock pulse supply. These test pulses also control a voltage source which is dependent upon them, and which supplies energy to at least one switching element in one of the two output channels. A fail-safe amplifier can be connected to at least one of the gate stages.