Telephone exchange switching state control unit - has common control with stores updated by cyclical scan of switching unit gated crosspoints and referred back to long-term store condition

摘要

Common control operating method is for a telephone exchange whereby all connections and switch states, through the switch block of the exchange, are scanned and information relating to their state is stored in the common control. Two stores are used for holding switch state information and each is updated by a cyclic scan of all switching equipment. The two-cycle scan attempts to avoid transitory errors due to interfering impulses etc. and employs a 'multiple last look' scan principle. In the telephone exchange the various switch units are controlled and interrogated by a common control which uses gated marker wires to obtain information about cross connections in the switchblock. Gated information updates stores in the common control but to avoid repeated scan of long duration connections, a store is used to hold the information relating to that call and is interrogated on a 'last look' basis by the common control.