An analogue/digital interface circuit is disclosed in which an integral bistable circuit has its state changed by the arrival of an incoming analogue signal, however transient, and irrespective of when it arrives relative to the clock signal driving the digital circuit. The use of a bistable (flip-flop) circuit enables each parth of the interface circuit to be traversed when scan test signals are applied to it. Concurrently with the application of such signals, an inhibition signal is applied to the analogue signal inlet to prevent the arrival of any subsequency analogue signals from changing the state of the signal-storage element.