CIRCUITRY

Circuitry comprises control circuitry to control an operating state of a data handling device of a set of two or more redundant data handling devices configured to perform identical data handling functions; the control circuitry being configured to control an operating state of the respective controlled data handling device as a state transition from a current operating state of that data handling device to a target operating state in response to the issue of a respective state change signal; the control circuitry comprising a detector responsive to issue of the state change signal in respect of a first threshold number representing some but not all of the data handling devices, to detect whether the state change signal is issued in respect of a further one or more of the devices so that a second threshold number of data handling devices is reached.