GB1403067A - Data transmission systems - Google Patents

Abstract

1403067 Digital transmissions; polling systems INTERNATIONAL BUSINESS MACHINES CORP 17 Oct 1972 47723/72 Heading H4P Two-way communication between a central processor 1 (Fig. 3) and a remote station 19 is through at least one intermediate station 17 or 18 which itself establishes data communication with the processor when it receives an end-oftransmission signal from the remote station 19. Thus each station in a chain 19, 18, 17 may transmit successively to the processor 1 over a single channel 8, in response to a single poll signal from 1 sent to remote station 19. In another chain of stations 12, 21, 13, 14, connected by a modem 15 to the channel 8, the station 21 is accorded a higher level of priority by making it responsive to end-of-transmission signals from either of the two end stations 13, 14, while making the latter responsive only to unique address and poll signals. Each station 21 (or 17, 18, 19) includes an outgoing transmitter and receiver (30, 28, Fig. 4, not shown) to pass the polling signal from the processor to the furthest station, and a return transmitter and receiver (38, 36) conveying to the processor the data transmitted by the remote station in response to the poll. When eventually the end-of-transmission signal from the adjacent downstream station is received (by 36) and identified by a decoder (42), a buffer register (24) is caused (by unit 26) to convey data (from 22) to a gate (44) and transmitter (38). When the station (21) is addressed by the processor to receive data therefrom, a decoder (34) recognizes the address and causes the unit (26) to make a gate (32) pass this data to the register (24) and the input-output device (22). In the event of failure, an emergency shunt (46) by-passes the station. If a downstream station fails, its "ready" signal (on line TR) disappears causing this station (21) to assume the role of end station.