Input parameters

Unless specified otherwise in the function block's description, the input parameters are read with the rising edge A rising edge is the transition of a digital signal from low to high. It is also called positive edge of the Execute input.

The input parameters can be as follows:

• Function Blocks with Execute
  

  These FBs will initiate execution on the rising edge of 'Execute'. Execution will continue until completion independent of the 'Execute' value (or values) following initiation. Once execution is complete, the function block can be rearmed or reengaged by introducing another rising edge of 'Execute'.

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  • Dual-Core limitation: Consecutive calls to the function block with repeating 'Execute' values within the same cycle will return an error code 76.
• Function Blocks with Enable
  

  These FBs will continuously be executed every PLC "Programmable Logic Controller" A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Used to synchronize the flow of inputs from (physical) sensors and events with the flow of outputs to actuators and events cycle, as long as the Enable remains high.

• Function with En
  

  This is very similar to ENABLE on Function A function calculates a result according to the current value of its inputs. A function has no internal data and is not linked to declared instances. blocks. But, as already explained in Difference between Functions and Function Blocks, functions are expected to complete in one cycle.

For the list of input parameters and its description for PLCopen A vendor -and product- independent worldwide association active in Industrial Control and aiming at standardizing PLC file formats based on XML Function/Function Blocks, see "List of Input Parameters"