Arrangement and method for switching the electronic subsystems of a common control communication switching system without interference to call processing

Claim 1

In a common control communication switching system wherein the common controls are duplicated and operated in synchronism, the common controls each including a logic unit portion and an associated memory portion, only one of said logic units being on line and communicating with the space shared subsystems of the communication switching system at any one time, a maintenance controller means for checking the operation of the logic units and memories and for providing output signals indicating the failure of one or both of the logic units or memories, an arrangement for switching the duplicated synchronously operating logic units and memories in the event of the failure of the on line logic unit or one of the memories without effecting the communication with the space shared subsystems comprising: (a) first latch means operable to set said logic units on line or on standby, said first latch means normally being operated to preset one of said logic units on line and the other one thereof on standby (b) means operated upon the coincident occurrence of an output signal from said maintenance controller means indicating the failure of said on line logic unit and a system timing pulse occurring during the time said on line logic unit is not communicating with said space shared subsystems to switch said logic units so that the on line logic unit is set on standby and the logic unit on standby is set on line; and (c) first gating means for gating said logic units to and in communication with said space shared subsystems coupled to and controlled by said first latch means to gate only said one line logic unit to and in communication with said space shared subsystems, whereby switching of the logic units in the event of a failure of the on line logic unit is controlled by said first latch means and is accomplished during the time that the on line logic unit is not communicating with the space shared subsystems so that the communication with the space shared subsystems is not affected.