Remote supervisory control system

Claim 1

A remote supervisory control system including a master station and a plurality of slave stations which are interconnected in a linear configuration and which share the transmission route connected to the master station and for which the presence and absence of data to be sent to the master station thereof are enquired by the master station wherein a master station is connected to a plurality of slave stations extending in a linear series interconnected sequence from the master station to an end slave station connected at the end location of the transmission route of said linear sequence, such that communication between said master station and said slave stations flows linearly in opposite directions through a communication path extending from said master station to said end slave station; said slave station connected at the end location of the transmission route is responsive to a polling signal issued from the master station such that responsive to the presence of data to be sent to the master station, the slave station transmits a code with a "busy" token specifying the data so as to send the code to a slave station at the next upper location in the direction opposite to the direction of the initiation of transmission of said polling signal transmitted from the master station to the slave station and that responsive to the absence of data to be sent to the master station, the slave station at the end location transmits a code in said opposite direction with a "free" token to a slave station at the next upper location; in slave stations connected at intermediate locations between said master station and said slave station at the end location, when a code with a "busy" token is received from a slave station at a lower location, the receiving slave station relays the entire code associated with the "busy" token in said opposite direction to a slave station at the further upper location or to the master station and when a code with a "free" token is received and there exist data to be sent to the master station, said slave station replaces the "free" token with the "busy" token and subsequently sends the code associated with the data and when there do not exist data to be sent to the master station, said slave station relays a code with a "free" token in said opposite direction to a slave station at the next upper location or to the master station.