Each value that is read or written by your Function Block Diagram is represented by a variable or a constant. Constant values are values that are fixed and are described in Add a Constant Value to a Function Block Diagram. Variable values change according to the data that is stored in your system and the calculations that are performed on it.
There are 2 types of variable:
- Internal variables are values that are used by the program but are not written to an item in the database. For example, values that are used in a conversion.
- Direct variables are values that are stored in the database, for example, a point value.
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