Data communication system

Claim 1

A data communication system having a master station and a plurality of slave stations arranged in hierarchical forms thereto and connected with a dedicated line allowing coexistence of analog lines and digital lines in a multidrop system, and the master station gathers information from the slave stations by a polling system, at least one of said slave stations being a first slave station provided between an analog line and a digital line, said first slave station comprising: (a) modem means, electrically and operatively connected to said analog line, for demodulating a first signal from the master station and modulating a second signal toward lower level slave stations and modulating a third signal as a response signal toward the master station from said first slave station, and (b) control means, electrically and operatively connected to said modem means for extracting a slave station discrimination number from a polling signal which is received from said master station through said modem means, determining whether said extracted discrimination number indicates the discrimination number of a lower level slave station with respect to said first slave station and outputting a carrier control signal for sending a carrier signal in accordance with the result of the extraction of the discrimination number, wherein; said modem means transmits said carrier signal to a line upon reception of said carrier control signal from said control means to send the response signal from the lower level slave stations to high level stations and also transmits the response signal to the higher level stations when the response signal is input from the lower level slave stations.