Patent GB-1245431-A (GB)
Title: Communication switching systems
Inventor: EWIN JAMES COE
IPC: H04Q3/545
Filed: 1968-10-17
Abstract: 1,245,431. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 17 Oct., 1968 [19 Oct., 1967], No. 49346/68. Heading H4K. In a telephone exchange controlled by a central data processor a scanner working asynchronously to the processor scans peripheral circuits such as lines, trunks &c. for changes in state and feeds state change data including the time at which each change occurs to an input buffer of the processor. Periodic interruptions of the processor to control scanning are thus avoided. The processor normally gives priority to the control of switching operations and only interrogates the buffer to detect off hook, dial signals &c. when it is free. The buffer is adapted to interrupt the processor only if it becomes full. The system described is of the type described in Specifications 1,081,811 to 1,081,817 and includes peripherals comprising line circuits 103L and trunk circuits 104, associated supervisory circuits 107 and 108, a scanner 110, a clock 132, a buffer 120 and a central processor 101. Supervisory circuit 107 for the line circuit 103L is identical to all other supervisory circuits and comprises a detector 107D which gives an output on one of two lines designates "0" and "1" in accordance with the state of its line circuit 103L, a flip - flop 107F which stores the state of the line circuit on a previous scan, a pair of "AND" gates 107-0 and 107-1 which compare the current and previous states, one or other "AND" gate being enabled in accordance with the direction of change, and two delay circuits via one or other of which any output from AND gate 107-0 or AND gate 107-1 as a result of a change is fed back to set the flipflop 107F to the new state. The feed back is effected via two synchronous wipers 110a and 110b (or electronic equivalent) of the scanner 110 when the wiper 110a steps to the enabled terminal C 103-0 or C103-1. The resultant pulse through the wiper 110a in addition to being fed back to the flip-flop 107F via the wiper 110b causes the address of the enabled terminal and the time as determined by a clock 123 to be entered into the buffer (shift) register 120. When the processor has time to spare it interrogates the shift register via a shift control 122, sorts the data for two changes of state relating to the same terminal and thus the same peripheral, and if data relating to two such changes are found the times of the changes are entered into registers 101A and 101B and subtracted at 101SV to give the duration of that state. A 0 to 20 millisecond duration signal is regarded as a transient and ignored, a 20 to 50 millisecond signal causes a trouble ticket to be printed, a 55 to 130 millisecond signal from a trunk is interpreted as a re-ring (backward) answering signal from a remote exchange, a 25 to 70 millisecond signal from a line is interpreted as a dial pulse, a 250 to 750 millisecond signal as a switch-hook flash and an over 750 millisecond signal as a disconnect signal. Where data relating to only one change of state relating to a terminal is found this data is entered into a store 101TM and read out again for use when the buffer is next interrogated. The processor is able to direct the scanner to a particular line via an address access circuit 115.