Abstract: A circuit for exchanging communications via a transmission line, including a detector for detecting a predetermined start-of-communication signal, a means for coupling the transmission line on the one hand to a transmit line to provide outgoing communications to the transmission line, and on the other hand to a receive line, to receive incoming communications from the transmission line. The detector is connected to the transmit line.

Abstract: A circuit for exchanging communications via a transmission line, including a detector for detecting a predetermined start-of-communication signal, a means for coupling the transmission line on the one hand to a transmit line to provide outgoing communications to the transmission line, and on the other hand to a receive line, to receive incoming communications from the transmission line. The detector is connected to the transmit line.

Abstract: In order to insure the protection of telephone set circuits when overvoltages generated from the telephone line occur, without impairing the operation of the set when hooking off the handset, the instant invention provides for a protection circuit incorporated into the integrated circuit fulfilling the main functions of the set. This protection circuit limits the current used by the integrated circuit top a first value (120 milliamperes) for the 250 milliseconds which follows the hooking off of the handset, then to a second value (60 milliamperes). If an overvoltage occurs, generated from the line, a time-delay of 100 milliseconds occurs before assigning a supplementary current limitation to 30 milliamperes. According to the invention, this time-delay may be as short as 100 milliseconds since it is initiated only if the first time period of 250 milliseconds is completed.