Patent GB-1237235-A (GB)
Title: A logic unit for translating dial telephone signals into control signals for switching circuits of an electronic time sharing exchange
IPC: H04Q11/04
Filed: 1968-10-29
Abstract: 1,237,235. Automatic exchange systems. SOC. ITALIANA TELECOMUNICAZIONI SIEMENS S.p.A. 29 Oct., 1968 [30 Oct., 1967] No. 51150/68. Heading H4K. In a "last look" scanning arrangement in which the data derived from a scan of an input is stored in coded form, read out during the next scan, updated in accordance with current input data and re-entered in the store for recirculation, each coded form takes at least six different values each of which designates that 0, 1 or 2 pulses of a sequence of periodic pulses, spaced apart by intervals of duration longer than a single dial pulse, have arrived since the last change of state of the associated input from either 0 to 1 or 1 to 0 was detected, and three different outputs, "dial pulse", "inter-digit pause" and "on hook" are produced in response to detection of corresponding change of state sequences. As shown; a time division multiplex signal D is inverted in a unit E and both D and #D are sampled by impulses M A  one to each time slot of the multiplex signal to give impulse trains P and A, respectively. These trains together with a sequence of periodic (exÓmination) pulses Z spaced apart by intervals of duration longer than a single dial pulse are applied to a logic circuit LS which also receives in synchronism with each pulse of the trains P and A a four-bit binary coded word U 4 , U 3 , U 2 , U 1  and its complement #U 4 , #U 3 , #U 2 , #U 1  emitted by a recirculating memory M. Each binary coded word is permanently associated with a time slot and each code combination represents a state of the line associated with that time slot. Code combinations representing digits 0, 1 and 4 designate that respectively at least two, one and no examination impulse or impulses Z have arrived since the associated subscriber loop opened while code combinations representing digits 5, 7 and 12 designate that respectively at least two, one and no examination impulse or impulses Z have arrived since the subscriber loop closed. The remaining code combinations are each associated with one of the above referred to combinations and may be passed through in going from that above referred to combination to another referred to combination, the sequence of such intermediate steps being dependent of the shape of the transients or switching noise at the ends of the dialling pulses. The logic circuit pulses one of sixteen output wires S 0  to S 15  corresponding one to each possible code combination at each time slot in accordance with wired AND gate logic (Fig. 6, not shown) to feed back a signal derived from the word U 4 , U 3 , U 2 , U 1  by updating in accordance with the inputs P, A and Z as determined by the wired logic. The resultant pulse signal is recoded to binary form at COD and entered in the store M for recirculation. An AND/OR logic circuit U receives the pulse signals Z, P, #U 4 , #U 3 , #U 2 , #U 1 , U 4 , U 3 , U 1  and gives an output M C  indicating that a dial impulse has been detected whenever code combinations corresponding to 8 or 9 are read out of the store, gives an output M F  signifying an inter-digit pause whenever states 12, 13 or 15 are read out and gives an output M L  signifying that the subscriber has gone back on hook whenever the state 0 is read out.