Operation

A DFB instance is executed as follows.

Step

Action

1

Loading the values in the input and input/output parameters. On initialization (or on cold restart), all non-assigned inputs take the initial value defined in the DFB type. They then keep the last value assigned to them.

2

Execution of the internal program of the DFB.

3

Writing the output parameters.
NOTE: The internal variables of DFBs are not reinitialized when using Build project online command after an input modification. To reinitialize all internal variables use Rebuild all project command.

Debugging of DFBs

The Control Expert software offers several DFB debugging tools:

  • animation table: all parameters, and public and private variables are displayed and animated in real-time. Objects may be modified and forced

  • breakpoint, step by step and program diagnostics

  • runtime screens: for unitary debugging