Patent GB-971514-A (GB)
Title: Electronic switching telephone system
IPC: H01L27/00
Filed: 1962-05-25
Abstract: 971,514. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. May 25, 1962 [May 29, 1961], No. 20203/62. Addition to 953,895. Heading H4K. In a switching system comprising a plurality of cascaded cross-point matrices for connecting inlets to outlets thereof, the outlets are marked cyclically, and an inlet requiring connection is only marked whilst an outlet is being marked, the markings initiating a plurality of self-seeking paths between the inlet and outlet, the completion of one such path disabling the others. As shown, Fig. 1, links 30, 31, 32 are enabled cyclically and if point x1 is marked by the subscriber A going off-hook during the time t1, say, when link 30 is enabled so that point x2 is also marked, a switching race through the free paths in matrices 21 occurs until a connection is completed between these points, whereupon a change in potential of point x2 busies the link. The link now receives and registers the dialled digits, and when the next instant t1 occurs it marks point y2 and also the appropriate tens and units lead 37, to cause the wanted subscriber's line circuit 36 to mark the point y1. A second switching race then occurs to complete the connection between the link and the wanted subscriber. Figs. 3 and 4 illustrate the link circuit 30. Pulses t1 are applied to the link via gates 304 and 443, and in the idle condition the output of the former gate is applied via 305 to x2. If a line is calling at this time, a path is established through the switching matrix and this causes a voltage change which operates the voltage change detector #V1, whose output is applied to device 322 which turns off immediately so allowing 306 to apply holding potential to x2 after t1 terminates. Device 322 in turning off also permits flip-flop 308 to change over, so applying holding potential via transformer 302. #V1 operates 323 after a delay to step the sequence circuit 415 to position 2 to enable the dial tone gate 414 and also the input gate 330 to the tens register 342. The dialled impulses representing the tens digit are detected by #V1 and fed via 330 to the store 342. Device 323 is released during the impulse train and on reoperation at the end it steps 415 to position 3 whereupon the units digits are received and stored in a similar manner, after which 415 goes to position 4. This enables gate 443 to pass the next t1 pulse, which opens gates such as 344, 346 to mark the wanted lines tens and units leads, and also marks point y2 via amplifier 430. A path between the wanted subscriber and point y2 is then established, the resulting current surge in transformer 44 setting flip-flop 431 to position B to cause tone ringing to be sent to the called subscriber. When the called subscriber answers the change in voltage is detected at 411 whose output operates a switching device 44 such as a bilateral transistor to complete the connection and also operates bi-stable device 409 to cut off the tone ringing. If the wanted line is busy no connection is made so that 431 is not set, but 432 is set and when t1 terminates 422 opens to enable the busy tone gate 421. When the calling subscriber hangs up #V1 turns 323 off immediately, and 322 turns on after a delay. 322 inhibits flip-flop 308 to remove the hold potential applied to x2 and enables gates 310, 312 to apply zeroizing pulses to registers 342, 345, after which 341 applies resetting pulses to 415. 322 also restores the remainder of the circuit. The switching elements may be PNPN diodes.