Variables

Variables are declared in one of the variable sections. A variable can be declared with

• an elementary data type or
• a user-defined type or
• a reference type or
• a user-defined type within the variable declaration.

A variable declaration consists of

• a list of variable names to be declared
• a ":" (colon) and
• a data type with optional variable-specific initialization.

VAR
    myVar1, myVar2: INT; // two variables with an elementary type
    myVar2: myType; // use a previously user-defined type
    myVar3: ARRAY [1..8] OF REAL; // use an immediate user-defined type
END_VAR

Initialization of variables

The default initial value(s) of a variable is (are)

1. the default initial value(s) of the underlying elementary data types
2. NULLif the variable is a reference,
3. the user-defined value(s) of the assigned data type; This value is optionally specified using the assignment operator := in the TYPE declaration,
4. the user-defined value(s) of the variable; This value is optionally specified with the assignment operator := in the VAR declaration.

Variable types

Variables can be defined in different sections of a program. The following table shows the different types of variables and their usage:

type	usage	definition
VAR	Internal within an entity (function, function block, etc.)	VAR END_VAR
VAR_INPUT	Input variable, not changeable within entity	VAR_INPUT END_VAR
VAR_OUTPUT	Output variable, not changeable within entity.)	VAR OUTPUT END_VAR
Access Variables	Used to connect program variables to HMI or external data sources	defined in the configuration section
Global Variables	Variables that are available throughout the entire project	defined in the configuration section
Config Variables	Variables that are used to give initial values to certain variables in different POUs	defined in the configuration section