Abstract: A method for avoiding interference with the "logic" section of an electronic central control unit by the voltages manipulated in a network of peripheral elements, for instance in a telephone switching system, is provided. The method according to the invention uses generators which transmit recurring test pulses along two-wire lines coupled by transformers with amplifiers delivering pulses, staggered in amplitude and time, into a network of peripheral elements. Depending upon the state of these elements pulses are retransmitted, or are not retransmitted, to the base of a bipolar transistor which opens or closes a two-wire line coupled by a transformer to a receiver of the central control unit.