Patent GB-990824-A (GB)
Title: Selection system
IPC: H03K17/60
Filed: 1961-08-11
Abstract: 990,824. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Aug. 11, 1961 [Aug. 12, 1960], No. 29084/61. Heading H4K. A hunting arrangement for seizing a free one of a group of circuits in a time-division multiplex exchange extracts from the identity of the called line codes to identify the wanted group and the first member of the group, a store being interrogated to obtain a code indicating the second member of the group so that if the first member is found busy the store may be interrogated again to obtain the address of the third member of the group in case the second member is busy, and so on. The arrangement concerns the seizure of a free line in a pbx group or a group of junctions or of a free signalling unit required for a call. In the time division multiplex exchange considered, each call is served by a register comprising one row of a magnetic core matrix, the contents of each row being staticized in sequence in common apparatus such as DNR, ADR, CLR, BLR and ENR, to enable each call to be supervised. When a register has accumulated in code the digits identifying a wanted subscriber, and supposing that this indicates a pbx group, the code is statized in circuit DNR and during the appropriate period of logical operations pursued during staticization, a "read-only " store MT (such as described in Specification 918,603) is addressed with the code to obtain, under interrogation by sinusoidal source V, further address codes staticized in circuits ADT and CLT which indicate the identity of the first line of the wanted group and an indication that a pbx group is involved, respectively. These codes are read out to circuits ADR and CLR in the register staticizing circuits and are stored in the register until the next staticization period. When next staticized a gate G 2  enabled by inverter I and the group indication from CLR passes the first line code from ADR to a " read-only " store MH which, when so addressed, provides a code staticized in circuit ADH to indicate the address of the second line of the group and a code staticized in ENH to indicate the position of the first line in a storage circuit LILI which records line conditions. The contents of ADH and ENH are transferred to the register staticizing circuits ADR and ENR and before these circuits are read back into the register the code in ENR addresses the storage circuits of LILI to obtain the state of the first line of the group which is set up in the register circuit BLR. When the register is staticized for the third time and supposing the first line of the group is busy, circuit BLR now disables gate G 2  and enables gate G 4  to address "read-only" store MH fromADR to obtain the address of the third line of the group which is passed through ADH to ADR, and to obtain the code locating the second line which is tested from ENR by way of ENH. Should BLR exhibit a busy state for this line also the third line is tested when the register is staticized a fourth time, and so on. When an idle line is found, BLR instructs the register to set up a connection to the line indicated by ENR. Should all the lines of the group be busy the store ADH is given a code when MH is addressed for the last line so that the register is instructed to connect busy tone should the last line be occupied. Specifications 904,232, 904,233, 977,420, 990,821, 990,822 and 990,823 also are referred to.