Edit Variables as Text using IEC 61131-3 Syntax

Using IEC 61131-3 syntax, variables are declared within structured blocks.

Each block begins with VAR, VAR_INPUT, VAR_OUTPUT, or VAR_EXTERNAL keyword and ending with END_VAR keyword (with no semicolon after).

This table provides the meaning of each keyword:

Keyword

Meaning

VAR

Memory variables.

Can be global, local, or retain depending on the edited group.

VAR_EXTERNAL

External variables.

Can be global or local 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.

Basic Syntax for Declaring a Variable

To declare a variable, enter its symbol followed by a colon (:) and its data type.

Data Type: STRING

If the data type is STRING, it must be followed with the maximum length in parentheses (e.g., STRING (255)). 

MyVar : BOOL;
MyString : STRING(255);

Read-only Attribute

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

CONSTANT VarName : DataType;

Declare an Array

To declare an array, the data type must be preceded by ARRAY [ dimensions ] OF.

  • There are at most three dimensions, separated by commas.
  • Each dimension is specified as 0 .. MaxBound (e.g., 0 .. 9). 
Array1 : ARRAY [0 .. 99] OF DINT;
Matrix : ARRAY [0 .. 9, 0 .. 9, 0 .. 9] OF REAL;

Single Variable Input Value

You can specify an initial value for single variables.

  • The initial value is entered after the data type and is preceded by :=.
  • The initial value must be a valid constant expression that fits the data type. 
MyBool : BOOL := TRUE;
MyString : STRING(80) := 'Hello';
MyLongReal : LREAL := lreal#1.0E300;

Additional Information and Description Texts

Variables may have additional properties and comment texts in the KAS-IDE.

Special directives are entered as IEC comments AFTER the declaration of the variable, to specify additional info.

These directives are available:

Directive

Description

(*$desc=Text*)

Variable description

(*$embed=Text*)

Variable embedded properties (the syntax is the one shown in the variable grid, in the "Property" column)

(*$profile=ProfileName*)

Variable embedded profile

(*$tag=Text*)

Variable tag (short comment)

Optional: Use // single line comments to enter the directives:

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