Distributed control system

A distributed control system comprising:

• a plurality of control devices;
• a process IO master device shared by the control devices and including:
• an output authority table comprising a plurality of fields with each field being an output authority for either (a) a different respective address of a plurality of addresses of an actual output area or (b) a different respective set of addresses of a plurality of sets of addresses where the plurality of addresses of the actual output area comprises the plurality of sets of addresses, and
• an output data memory having:
• areas for storing data outputted from the control devices, and
• the actual output area different from the areas for storing data outputted from the control devices, the actual output area comprising the plurality of addresses;
• and
• a plurality of process IO modules connected to the process IO master device and each connected to a sensor and an actuator, wherein:
• the output authority table provides an authority that determines the control device of which output data is to be adopted and stored in the actual output area for output to the actuator, for each of addresses corresponding to the actuators and the areas, and
• the process IO master device is configured to, in response to a determination to switch from a first control device to a second control device of the plurality of devices, update the output authority table to indicate a hold for an address of the output authority table associated with the first control device such that the address is not updated until the hold in the output authority table is updated to indicate control by the second control device.