GB1237073A - Improvements in or relating to data link communications - Google Patents

Abstract

1,237,073. Synchronous communication systems. PLESSEY CO. Ltd. 21 Oct., 1968 [21 July, 1967], No. 33659/67. Heading G4H. In a communication system data is transmitted as a sequence of information pulses alternating with synchronization pulses, the receiver including scanning means responsive to the synchronization pulses to direct the information pulses to receiving means. A group of switches 5 is sampled by a ring counter 4 advanced by pulses from a clock 7. The synchronization pulses are negative and the information pulses are positive to represent " O " and zero to represent " L", as shown in Fig. 2. At the receiver the synchronization pulses are detected at 12 and passed via a unit 13 to step the distributer 6 which is an eight-stage ring counter. The information pulses pass via the distributer 6 to corresponding sections of a store and are indicated by the lamps of an indicator 10. The counter 4 has eight stages, the last three sending no signal so that a blank interval is provided during which the counter 6 is reset to its eighth position. For this purpose a blank space detector at 13 opens gate 8 to allow pulses from a clock 9 to pass to the counter. When the counter 6 reaches the eighth position, the gate 8A is disabled to prevent further counting. The first synchronizing pulse from the transmitter steps the counter 6 to the first position and the following information bit passes to the appropriate position of the store. If, due to spurious pulses, the counter is returned to its initial position when the long period of no signal is detected at 13. The store may be arranged to accept information bits only if they have been repeated three times in three consecutive cycles. Instead of using pulses of opposite polarity, bursts of different frequency may be used.