Polling system for a duplex communications link

Claim 1

A method of providing more efficient use of a single communication channel of a controller/remote terminal unit link serving a multiplicity of terminal units, each unit having a permanent and unique address and comprising logic circuitry and memory, and comprising the following steps: assigning to each said terminal unit address a permanent position in a queue of addresses stored in the memory of the controller; the controller continuously tagging each terminal unit address in the queue as active or inactive, where "active" means that the unit is presently operating upon data or has been operating upon data within a predetermined period of time; the controller transmitting all of the terminal unit addresses which are tagged as active units, omitting the addresses of all units tagged as inactive units, in a sequence determined by the queue of addresses; the controller transmitting the addresses of a predetermined number of said inactive units, the choice of said units being determined by the queue of addresses; the controller listening during said transmissions to both active and inactive units for the controller address to be received from any one terminal unit within a fixed time period following the transmission by the controller of the address of said one terminal unit, said fixed time period ending later than the beginning and earlier than the end of the next subsequent address in the transmitted sequence; any one of the terminal units responding to said respective assigned address by transmitting the controller address followed by a data message; the controller recognizing that reception of the controller address during said fixed time period is a response from that terminal unit having the address immediately preceding the address being transmitted at the time of controller address detection; upon such reception, the controller interrupting the sequence of said address transmissions, storing the received predetermined message and any immediately subsequent data from the responding terminal unit; the controller processing said predetermined message; and the controller resuming transmission of the sequence of messages, beginning with the address which was previously interrupted.

Claim 2

A method of providing more efficient use of a single communication channel of a controller/remote terminal unit link serving a multiplicity of terminal units, each unit having a permanent and unique address and comprising logic circuitry and memory, and comprising the following steps: assigning to each said terminal unit address a permanent position in a queue of addresses stored in the memory of the controller; the controller continuously tagging each terminal unit address in the queue as active or inactive, where "active" means that the unit is presently operating upon data or has been operating upon data within a predetermined period of time; the controller transmitting all of the terminal unit addresses which are tagged as active units, omitting the addresses of all units tagged as inactive units, in a sequence determined by the queue of addresses; the controller transmitting the addresses of a predetermined number of said inactive units, the choice of said units being determined by the queue of addresses; the controller listening during said transmissions to both active and inactive units for the controller address to be received from any one terminal unit within a fixed time period following the transmission by the controller of the address of said one terminal unit, said fixed time period ending later than the beginning and earlier than the end of the next subsequent address in the transmitted sequence; any one of the terminal units responding to said respective assigned address by transmitting the controller address followed by a data message; the controller recognizing that reception of the controller address during said fixed time period is a response from that terminal unit having the address immediately preceding the address being transmitted at the time of controller address detection; upon such reception, the controller interrupting the sequence of said address transmissions, storing the received predetermined message and any immediately subsequent data from the responding terminal unit; the controller processing said predetermined message; and the controller resuming transmission of the sequence of messages, beginning with the address which was previously interrupted.