GB1198921A - Improvements in or relating to Circuit Arrangements for Identifying Feeder Lines in Telecommunications Exchange Systems - Google Patents

Abstract

1,198,921. Automatic exchange systems. SIEMENS A.G. 4 March, 1968 [2 March, 1967], No. 10313/68. Heading H4K. An electronic line finder comprises a closed ring of gates into which a hunting potential is injected when a demand potential appears on one of the lines associated respectively with the gates, coincidence of the demand and hunting potentials at one of the gates causing hunting to stop and marking of a bi-stable circuit associated with the gate to be effected. The finder is of particular use in a code-multiple telegraph exchange where it is necessary to connect lines to trunks at high speed with little probability of incorrect connections arising from the occurrence of simultaneous demands. Methods of ensuring that only one demand at a time is met include:-interconnecting the output bi-stable circuits by gates so that at the end of a finding action only that bi-stable of lowest order remains set (Fig. 2, not shown); interconnecting the ring of gates to the output bi-stables by additional bi-stables so that if the hunting potential manages to get through one of the gates even though it should be inhibited due to the presence of a demand potential thereat, the further bi-stable will lock-out the output bistable (Fig. 3, not shown); and locking-out further demand potentials until the current one has been processed. The necessary logic, for interconnecting line finders operating on a coordinate basis, viz, when more than 10 subscribers are involved and a minor modification involving the connection of the last gate in a lower order ring to the first gate in a higher order ring rather than to its own first gate, is described with reference to Figs. 4-6 (not shown). Operation, Fig. 1.-It is assumed that output bi-stable Al is set, i.e. its output is on #a1 and that a demand potential appears on e3. A central control detects, by means not shown, the presence of the demand potential and applies a "call-up" pulse to bi-stable Z1. The "set" output of the latter then causes a pulse, of length equivalent to the transit time through the ring of gates D4-B1, to be supplied from logic F, T1, T2 to each of the gates E1-E4, gate M being opened by the demand potential so as to permit logic F to operate. Consequently E1 conducts (both inputs marked) and injects a hunting potential into the ring of gates D4-B1. This potential is stopped at B3 due to the presence at the second (left-hand) input thereof of the demand potential e3. Simultaneously gate C3 opens in order to set A3 and to reset Z1. (Al was reset by the opening of gate E1). The identity of A3 and hence of the calling subscriber can be transmitted to central control using a 1-out-of-n to binary code converter (not shown). In addition the setting of A3 is used to inhibit the demand potential on e3. NOR logic is used throughout.