Editing variables as text using IEC61131-3 syntax

Using IEC61131-3 syntax, variables are declared within structured blocks. Each blocks begins with VAR, VAR_INPUT, VAR_OUTPUT or VAR_EXTERNAL keyword and ending with END_VAR keyword (with no semicolon after). Below is the meaning of each keyword:

Keyword	Description
VAR	Memory variables. Can be global, local or RETAIN depending on the edited group.
VAR_INPUT	Input parameters of a block. Available only when the edited group is a UDFB.
VAR_OUTPUT	Output parameters of a block. Available only when the edited group is a UDFB.
VAR_EXTERNAL	External variables. Can be global or local depending on the edited group.

Basic syntax for declaring a variable

To declare a variable, simply enter its symbol, followed by ":" and its data type. If the data type is STRING, it must be followed the maximum length between parenthesis.

Example

MyVar : BOOL;
MyString : STRING(255);

To indicate that a variable has the read only attribute, insert the CONSTANT keyword at the beginning of the variable declaration:

CONSTANT VarName : DataType;

To declare an array, the data type must be preceeded by ARRAY [ dimensions ] OF. There are at most 3 dimensions, separated by comas. Each dimension is specified as 0 .. MaxBound.

Example

Array1 : ARRAY [0 .. 99] OF DINT;
Matrix : ARRAY [0 .. 9, 0 .. 9, 0 .. 9] OF REAL;

Additionaly, you can specify an initial value for single variables. The initial value is entered after the data type, and is preceeded by ":=". The initial value must be a valid constant expression that fits the data type.

Example

MyBool : BOOL := TRUE;
MyString : STRING(80) := 'Hello';
MyLongReal : LREAL := lreal#1.0E300;

Additional information and description texts

As a variable may have additional properties and comment texts in the Workbench Studio, we use special directives entered as IEC comments AFTER the declaration of the variable, to specify additional info. The following directives are available:

Directive	Description
($tag=Text)	Variable tag (short comment).
($desc=Text)	Variable description.
($profile=ProfileName)	Variable embedded profile.
($embed=Text)	Variable embedded properties (the syntax is the one shown in the variable grid, in the Property column).

You can also use "//" single line comments to enter the directives:

//$tag=Text
//$desc=Text
//$profile=ProfileName
//$embed=Text

Editing variables as text using IEC61131-3 syntax

IEC 61131-3 Automation platform > IEC 61131-3 Programming Environment > Variable Editor > Editing variables as text > Editing variables as text using IEC61131-3 syntax

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