Abstract: A smoke and fire detection system wherein a central controller transmits data to remote transponders on a voltage supply line by pulse code modulation (PCM) of the supply voltage, and the transponders communicate with the controller by pulse width modulated (PWM) current pulses over the voltage supply line. A transmitter in the controller supplies a nominal operating voltage to the transponders and transmits a data word comprising a plurality of data bits to the transponders over the line. The transmitter generates each data bit by switching the voltage supplied to the line from the nominal operating voltage to a first voltage corresponding to a first logical level or a second voltage corresponding to a second logical level. A decoder in each transponder derives the transmitted data word.

Abstract: A smoke and fire detection system wherein a central controller transmits data to remote transponders on a voltage supply line by pulse code modulation (PCM) of the supply voltage, and the transponders communicate with the controller by pulse width modulated (PWM) current pulses over the voltage supply line. A transmitter in the controller supplys a nominal operating voltage to the transponders and transmits a data word comprising a plurality of data bits to the transponders over the line. The transmitter generates each data bit by switching the voltage supplied to the line from the nominal operating voltage to a first voltage corresponding to a first logical level or a second voltage corresponding to a second logical level. A decoder in each transponder derives the transmitted data word.