COMMUNICATIONS SYSTEM AND REMOTE SCANNER AND CONTROL UNITS

1,229,814. Digital transmission systems. BURROUGHS CORP. 5 July, 1968 [12 July, 1967], No. 32280/68. Heading H4P. [Also in Division G4] A digital transmission system comprises a central data processing station 72 and a number of way-stations 1-15 connected to two pairs of common channels 76, 76a. Each way-station includes a number of substations 74 each of which can communicate with the central station via one or other of control units 70. Via either control unit in a way-station one substation may receive data while another transmits. Transmission from the central station is continuous, idle, poll, or synchronizing signals being sent when no message is to be sent. Characters are sent serially bit by bit and have a parity check bit. When the central station has a message to transmit it sends a start of message signal followed by an address code indicating the required way-station and the address of the required sub-station. The control unit 70 in the required way-station selects the called substation and forwards to it the message which follows the addresses. When the central station has no message to transmit it may poll the way-stations. It sends first a start of poll signal and then the address of a way-station. The way-station address signal enables the appropriate control unit 70 which starts the associated data set 80, sending three sync. characters to it which it transmits to the central station to synchronize it. When the data set has indicated to the control unit that it is ready the control unit scans its sub-stations 74 in sequence under the control of a counter. If a sub-station has a message to transmit the control unit stops the scan and sends to the central station a start of message signal followed by the address of the sub-station and the way-station. The message follows. At the end of the message the control unit sends an end of message signal and restarts the scan. If no sub-station has a message to send the control unit indicates this to the central station. The duration of each message may be limited. If the control unit detects a parity error in the message it replaces the faulty character by an error-indicating character. The addresses of the control units are manually adjustable by switches. If a preset number of adjacent sync. signals is received from the central station the clock circuitry in the control units is pulled into synchronism.