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Entry type: FAQ Entry ID: 52258437, Entry date: 12/28/2015

How do you define the constants in an S7-SCL program in STEP 7 (TIA Portal)?

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In Step 7 V5.x you can only define local constants in the declaration part of the SCL block code and use it in the program. Contrarily, STEP 7 (TIA Portal) differentiates between local and global user constants that you can define in the block interface or in the PLC tags.

In STEP 7 V5.x you can define the local constants in the declaration part of the SCL block code and use them in the program as shown in Fig. 1.

Fig. 1

In STEP 7 (TIA Portal) it is not possible to define constants in the declaration part CONST/END_CONST of the SCL program code.

This is how you define the constants in STEP 7 (TIA Portal) V13 and higher:

  • You define the local user constants in the block interface of an FC/FB under "Constant" and you can then use them in the block program. Here you must define a data type for the use constants.

    Fig. 2 
  • You define the global user constants, which are to be available CPU-wide, in the PLC tags in the "User constants" tab. Also when defining the global user constants you must define the data type.

    Fig. 3
Only use local constants within a block. In this way the block remains universal and can be used in a library.

Creation Environment
The screens in this FAQ response were created with STEP 7 (TIA Portal) V15.0 and STEP 7 V5.6.

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