Abstract: This invention is concerned with an interface for a computer system. This interface is characterized in such a way that it includes an assembly of elements (C2, C2') capable of performing an AND function, controlling modules (K1, K1') for monitoring the function of these elements (C2, C2'), the outputs of which modules are tied to a command system associated with the computer system D1, D1'), and means (K2, K2') to test the monitoring modules (K1, K1'), the command sytem being equipped with means to compare the states of the elements (C2, C2') that perform and AND function, as indicated by the control modules (K1, K1') with the command state. The warranting, means to inhibit the sending of a command signal is inhibited when the two states do not match. The invention is applicable to situations where a security interface is required.

Abstract: The state of an all-or-none modulated useful signal subjected to a perturbed environment is determined, on reception, through the use of non-modulated reference signals subjected to the same environment. The reference signals have respective frequencies neighboring that of the useful signal and the same initial amplitude so that all of the signals are attenuated in the same manner by environmental perturbations. By comparing against a threshold reference value the differences between the respective amplitudes of the received reference signals and the amplitude of the received useful signal, the "all" and "none" states of the useful signal are accurately determined irrespective of the effect of perturbed environment on the amplitude of the useful signal.