Abstract: A central controller (104) for a multipoint polling system arranged to collect inquiry messages from data terminals (102a-n, 103a-n) for processing by a data base (101) and for distributing response messages to the terminals, the several terminals using different communication protocols. The controller includes a RAM memory (203) which stores a list of items, each item identifying a terminal and the type of protocol used thereby, a ROM memory (202) which stores an instruction set for each protocol type and a microprocessor (201) which sequentially accesses each item on the list to poll the associated terminal and accesses the instruction set identified in the item to control sending and receiving equipment to query and intercommunicate with the selected terminal in accordance with the accessed instructions.

Abstract: Echo propagation is prevented on four-wire signaling path to two-wire signaling path connections. A first transmission path portion is extended from the receive leg of the four-wire signaling path to the transmit leg and a second transmission path portion is extended from this point to the two-wire signaling path, the first and second transmission path portions thereby forming a bidirectional path carrying signals from the two-wire signaling path and from the receive leg. Detection circuitry is located in the first transmission path portion and develops a voltage signal which determines the direction of signal transmission between the four-wire and two-wire signaling paths. Echo propagation is prevented during signal transmission from the four-wire signaling path to the two-wire signaling path by opening the transmit leg of the four-wire signaling path.