Patent GB-1020381-A (GB)
Title: Improvements relating to automatic telephone exchange systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1962-01-02
Abstract: 1,020,381. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 16, 1962 [Jan. 2, 1962], No. 166/62. Heading H4K. In an automatic exchange system incoming junctions are scanned to feed to a common pulse highway indication of the closed or open loop condition of the junction to signal to one of a number of registers indications representative of a wanted line, said registers being arranged to receive in digital form the identity of the calling junction on initial seizure of the register. Seizure of register.-The scanner SC provides a repetitive cycle of 400 scanning intervals, one per junction, each scanning interval being divided into four basic periods. The first period is used to step a 400 point counter in the scanner, and the third period is used to pulse the gate G of the junction whose identity is present in the counter. The counter comprises a " hundreds," " tens " and " units " counter the first two counting up to ten and the last up to four. The first and last of these are used to determine 40 pulse positions each pulse in one of these positions being applied to ten gates, which are made effective in turn by the tens counter to pass their outputs to PH. If the line relay in the incoming junction relay set I/CJRS indicates a looped condition the gate G is opened to pass a pulse, via the highway PH, to the pulse inhibitor circuit PI. The latter has a first and second lead connected to all the registers and an inhibit lead fed from all the registers, the latter being effective to inhibit only the output on the second lead. Each time the scanner counter is set, its setting is fed to all the registers and there compared with the calling line identities, and if identity occurs in any of these registers an inhibiting potential is fed to PI to suppress the output on the second lead to prevent a further register being seized. In the present instance there being no such inhibition the pulse on the second lead is admitted to a pre-allotted register. This pulse then gates the calling line identity from the scanner counter into the calling line store of the register. The pulse also sets a busy trigger whose output steps the allotter AL. Reception of digits.-Each register is allocated one of the 40 pulse positions mentioned above. It is also provided with a bi-stable circuit which receives s resetting pulse during the first basic period of each scanning interval. When the pulse position associated with the register occurs (during a third basic period) the bi-stable circuit is set to enable a gate to pass a pulse during the fourth basic period which gates the line identity stored in the register to the scanning circuit thereby causing the gate G to pass a pulse or not (during the fourth basic period) to the highway PH depending whether or not the loop is closed or open. This pulse received over the first lead from PI passes via a gate (enabled by the gate associated with the above mentioned bi-stable circuit) to a lead feeding the circuits used for storing the dialled impulses. These pulses are received on a bi-stable circuit operable on receipt of these pulses in the fourth basic period and reset in the following second basic period. The outputs of this bi-stable circuit operate on a second bi-stable circuit to cause it to remain set whilst pulses are received and reset when pulses are not received corresponding to the closed and open condition of the loop. The output of the second bi-stable circuit drives a counter and also disables a timing device as long as this bi-stable circuit is repeatedly changing over. When it stops the timing device operates to deliver a pulse to two gates. The first of these is open if the bi-stable circuit indicates loop closed and passes a pulse causing the stored digit to be transferr:d to a denominational store and prepares for the receipt of the next digit. The second gate is open if the loop is open (indicating an abandoned call) and passes a pulse to cause release of the register. When all the digits are received the register seizes a line identifier and passes the identities of the incoming line and the wanted line thereto, and the call is set up as described in Specification 939,336.