Patent GB-981337-A (GB)
Title: Improvements in or relating to time division multiplex switching systems
IPC: H04Q11/04
Filed: 1961-06-09
Abstract: 981,337. Automatic exchange systems. SIEMENS & HALSKE A.G. June 9, 1961 [June 10, 1960; March 17, 1961], No. 20934/61. Heading H4K. A time division multiplex exchange having means for allocating any one of a plurality of pulse positions to any subscriber, which pulses effect the connections of the subscribers to a speech multiplex point, comprises also a plurality of receivers capable of receiving dialling information from the subscribers in the form of multi-frequency code signals, each receiver being capable of being allocated a pulse position, the pulses of which connect the receiver to the speech multiplex point. As shown subscribers Tn1 . . . Tnx are interconnected by gates S1 . . . Sx and multiplex point SM, the calling subscribers gates being opened in the phase allocated to the call by a pulse inserted in appropriate combinations of circulating stores Ua, the stores Ub serving the same purpose for the called subscriber. Allocation of a digit receiver is controlled by combinations of circulating stores Uc. A register H for the identities of the receivers is stepped cyclically once per two multiplex cycles. In the first of these cycles, a comparator Vc compares the identity of the address stored in H with that stored in any pulse position for the same address in Uc. An output from the comparator indicates that the receiver in question is busy and prevents the control circuit E from allocating it. If it is free however, then during the next multiplex cycle, the control circuit emits a pulse in the calling subscriber's phase to the gate Sd which thus inserts the address of the receiver in Uc at that phase. Dialled digits are sent as combinations of voice frequencies and these are gated into a voice frequency receiver such as Z 1  by pulses from Uc opening gate Z 1  in the calling subscriber's phase. Each digit is stored in Z 1  long enough for it to be scanned by a device F, fed with the receiver identities received from store H, when it is admitted to the device M. The required phase of the call is obtained by comparison between Uc and H at Vc which emits a corresponding pulse to the control circuit E, which applies the pulse at the same phase in a succeeding cycle to gate Sg. The digit is passed thereby to the distributer Q, which has a set of code leads for each digit, there being a set of delay lines in Ub corresponding to each digit. The store Ub emits a signal for each phase indicative of the number of digital positions stored and this is used by the control circuit E to determine which output of the distributer Q is to be used, and the digit is correspondingly entered into Ub. The function of the device M is to convert the incoming multifrequency code to binary form for storage in Ub. The device may also carry out plausibility checks on the coder. Arrangements may be provided either for enabling or for connecting up a digit receiver only when a digit is dialled. To this end the subscriber's set is arranged to disconnect the microphone and open the loop temporarily either just before or during the frequency-code-sending, to inform the control circuit E that a digit receiver must be either enabled or connected up, the pauses between the digits being used either to discriminate between one digit and the next in the one case, or to disconnect the receiver in the other case. The digit receivers may also incorporate timeout circuits. The circulating store Uc may be provided with a counter for counting the number of phase positions occupied during a cycle, and hence to determine the degree of occupancy of the group of receivers at any time. Specifications 981,335, 981,336, 981,338 and 981,339 are referred to.