Modem ringing supression circuit

Abstract

An automatic telecommunication system includes a central location and at least one remote location where a data reporting system including a modem is situated. The central location establishes communications over the switched telephone network to the modem coupled to a telephone line at the remote location. At least one telephones is also connected to the telephone line at the remote location. Circuitry is provided for suppressing ringing of the telephone when the central location initiates a call to the modem at the remote location. The circuitry includes a microprocessor for controlling the modem to respond to incoming ringing signals on the telephone line only during a predetermined time window. The circuitry also includes an arrangement for detecting a ringing signal on the telephone line and delivering an input to the microprocessor indicating ringing. The microprocessor delivers an output if the ringing occurs during the predetermined time window. Circuitry is responsive to the microprocessor output to drive the modem to go off-hook. A circuit driven by the microprocessor establishes a load access the telephone line when the modem goes off-hook for a predetermined time period to essentially short circuit the telephone line for a period of time sufficient to allow ring trip on the telephone line, thereby preventing any ringing of telephones connected to the telephone line.