TELECOMMUNICATION EXCHANGE

1,235,154. Automatic exchange systems. ERICSSON TELEPHONES Ltd. 3 March, 1969 [8 March, 1968], No. 11512/68. Heading H4K. A telephone exchange includes a cyclic scanning store C which stores subscriber numbers and is pulsed to cyclically scan the lines corresponding to the stored numbers and supply an output signal to these lines. Wanted numbers are stored in register R and are compared with the number which the store C is instantaneously scanning. If they are the same, the scanning store position is frozen and the output signal applied to the line for a prolonged period. Gate G1, when enabled, allows pulses from generator P to advance the store C so that a signal is applied to each subscriber line terminal L in turn. Each terminal L contains a delay device d which is normally in circuit unless shunted by line relay contact l, the delay of device d being greater than the duration of the output signal from store C. A transistor may replace the line relay contacts. Calling condition.-Line relay contact I closes to route the output signal on line o through line c to routing equipment E and marks the line terminal on lead r. Equipment E marks routes through switching network S and returns a suspend signal to gate G3 which disables gate G1 and holds the output signal on line o. The switching network S establishes a route, opens contact l and signals equipment E to terminate the suspension signal so that store C is again supplied with pulses and resumes scanning. Called condition.-The number of the wanted line L is stored in register R and sent to routing equipment E and to equivalence gate G2 which compares the number in the register with the number of the line being scanned by store C. When these numbers agree, a pulse is sent to gate G3 whose output disables gate G1 to stop store C. The output signal on line o is prolonged and delay device d operates to supply a command signal to equipment E which establishes a route through switching network S. When the route is established, the register is cleared which removes the disabling signals so that store C is again supplied with pulses and resumes scanning.