21 - What is scheduling?
Function block execution and communication is scheduled to optimise control and communication efficiency. It may be used to ensure that blocks are executed in the correct order. The sequential passing of dynamic time critical function block input and output data is called operational traffic. This traffic and the execution of the function blocks is scheduled by the system so as to occur on a precisely period basis with a minimum delay thereby achieving optimum closed loop control performance. Scheduling allows the user to control the order and also the frequency of execution of a block.
Without scheduling the loop dead time will most likely be longer than the time it takes to communicate the operational traffic on the Fieldbus network. Another reason is that without scheduling the blocks may be executed in the wrong order.