Introduction to Industrial Automation

Figure 7.12  Graphical symbol of the comparison instruction (≥) of integers in LAD language.

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  Introduction to Industrial Automation

to take place occasionally when a condition occurs. Some examples of call instructions for a POU 

are the following ones:

 

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CALL FC 10

 

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CALL FB25, DB1

 

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CALL FB25, DB2

After the FB or FC is called via the CALL instruction, the CPU leads the execution of the 

program to the next instruction after the CALL instruction. The calling of a POU is accompanied 

by the introduction of certain information and the declaration of variables, as described in Section 

7.3. Since the analytical way to call a POU and the corresponding introduction of the required 

data depends on the manufacturer of the PLC and the specific software environment for program-

ming, there will be no further analysis of this topic. In a similar way, the call of a POU in the FBD 

or LAD language is implemented by inserting the elements into a graphic block.