GB1521273A - Communications system - Google Patents

Abstract

1521273 Selective signalling GENERAL SIGNAL CORP 2 Oct 1975 [21 Oct 1974] 40408/75 Heading G4H In a communication system including a master station and at least one remote station, the remote station stores (in a first memory) and checks data received from the master station and if correct transfers it to a second memory from the first memory, and the first memory is then cleared, and to permit both pulsed and latched outputs from the second memory to controlled devices, the (cleared) states of the first memory are then transferred into the second memory at those bit positions for which associated auxiliary switches are closed. An auxiliary switch is provided for each bit position or each group of bit positions, the auxiliary switches being controlled manually or from the master station. Thus each control output will be pulsed or latched according as the associated auxiliary switch is closed or open respectively. The master station addresses a remote station and sends control words, the addressed station responding with its address and indication words, polynomial checks words being used in both directions. The checking in a remote station referred to at the beginning above is detection of error using these words, and detection of parity, over-run and framing errors to set bits in an error register in the absence of respective errors. Absence of received data for a predetermined time resets the whole error register (i.e. simulates all errors). A local alarm signal is produced if the remote station does not transmit any data for a predetermined time. To permit two master stations to each control the same devices, memories &c., are provided for each master station in the remote station, the outputs of the second memories being passed via tri-level gates and commoning connections to the controlled devices. Each tri-level gate passes the 1 or 0 from the second memory except when a bit in the other second memory causes it to exhibit a high impedance. Thus either master station can prevent the other from controlling the devices.