Telecommunication exchange employing cross point switches

1,131,974. Automatic exchange systems. ERICSSON TELEPHONES Ltd. 12 July, 1967 [26 May, 1966], No. 23685/66. Heading H4K. Each matrix of a relay cross-point switching system has a so-called mark-extension circuit, such as can be seen in Fig. 2, the corresponding matrix being shown in Fig. 1; the mark extension circuit having terminals II-14 corresponding to each inlet row of the matrix, a mark on any such terminal indicating that a path is required over the corresponding inlet and, if the path is not marked busy by potential on the P-wire of the inlet, causing a switching device such as one of the relays E1-E4 to operate and extend earth over a Zener diode Z to the socalled reservation wire RS of the matrix row to permit subsequent operation of the cross-point relays in that row, and causing the operation of a switching device such as relay F to extend forward markings to the matrix mark-extension circuits of the next stage by way of leads 01- 06. When, by means not disclosed, one of the marked paths is selected for use, current is drawn over the hold-wire H of a column and finds earth over the cross-point relay winding in the row the reservation wire of which is connected to the Zener diode Z in the mark-extension circuit. Once the cross-point relay has operated, the, P-wire is connected to the markextension circuit and disables the operated relay from the set E1-E4 to release the mark-extension circuit. The relays E1-E4 are connected in a chain with diodes d12, d13 to d42, d43, so that the relay of highest denomination locks out relays beneath it. As an alternative, and as shown by the addition of dotted line circuits, the chain may accept the first mark to arrive and lock out later marks. A delay circuit DL times a period beyond which a relay J operates to release the mark extension circuit if normal operations have not been completed. The relays E and F may be replaced by transistor switching circuits (Fig. 3, not shown).