Redundant device control unit

An industrial, digitally controlled processing system including two nominally identical electronic devices connected in the system in a manner such that one of the devices functions as an active device in the system and the other device functions as a standby device, in which each device includes a back-up control unit including an optical fiber link for establishing communication between the device and the other nominally identical device, the unit being operative for determining whether the device is presently functioning as an active or standby device and for receiving signals indicating whether the other nominally identical device is functioning as an active or standby device, and for synchronizing the operation of the device with that of the other nominally identical device, and having a switch responsive, when the device is functioning as the standby device, to the occurrence of a failure in the other nominally identical device for causing the device to begin operating as the active device.