Variable declaration: Where and how?

You can declare variables at the following locations:

Declaration part of a POU

The “Declare Variable” dialog helps you with this.

TIP:

If you define a variable in the tabular declaration editor, the correct syntax is automatically produced.
Declaration part of the GVL or NVL editor
I/O mapping configuration of an I/O device object

Syntax

( <pragma> )*
<scope> ( <type qualifier> )?
    <identifier> (AT <address> )? : <data type> ( := <initial value> )? ;
END_VAR

	Declaration	⮫ “Using the Declaration Editor ” ⮫ “Dialog: Using the Declare Variable ” ⮫ “Command: Auto Declare ”
<pragma>	Pragma (none, one, or multiple) Note: By adding a pragma, you can affect the behavior and the properties of one or more variables.	⮫ “Using Pragmas ” ⮫ “Pragmas ”, ⮫ Further information
`‎<scope>‎`	Scope `‎VAR‎` `‎VAR_CONFIG‎` Note: If variables with incomplete address information are declared in function blocks (for example, `‎AT %I*‎`), then the variables in the variable declaration `‎VAR_CONFIG‎` have to be completely declared. You can access these variables in a local instance only when this is done. `‎VAR_EXTERNAL‎` `‎VAR_GLOBAL‎` `‎VAR_INPUT‎` `‎VAR_INST‎` `‎VAR_IN_OUT‎` `‎VAR_OUTPUT‎` `‎VAR_STAT‎` `‎VAR_TEMP‎`	⮫ “Variable: VAR ” ⮫ “Variable: VAR_CONFIG ” ⮫ “Variable: VAR_EXTERNAL ” ⮫ “Variable: VAR_GLOBAL ” ⮫ “Object: GVL – Global Variable List ” ⮫ “Variable: VAR_INPUT ” ⮫ “Variable: VAR_INST ” ⮫ “Variable: VAR_IN_OUT ” ⮫ “Variable: VAR_OUTPUT ” ⮫ “Variable: VAR_STAT ” ⮫ “Variable: VAR_TEMP ”
`‎<type qualifier>‎`	Type qualifier `‎CONSTANT‎` `‎RETAIN‎` `‎PERSISTENT‎`	⮫ “Variable: CONSTANT ” ⮫ “Variable: RETAIN ” ⮫ “Variable: PERSISTENT ”
`‎<identifier>‎`	Identifier, variable name Note: The rules listed in the chapter "Identifiers" have to be followed without exception when assigning an identifier. In addition, you will find recommendations for uniform naming.	⮫ “Identifier Designation ”, ⮫ Further information
`‎AT <address>‎`	Assignment of an address in the input, output, or flag memory range (I, Q, or M) `‎AT % <memory area prefix> ( <size prefix> )? <memory position>‎` Example `‎AT %I* // Incomplete address‎` `‎AT %I7.5‎` `‎AT %IW0‎` `‎AT %QX7.5‎` `‎AT %MD48‎`	⮫ “Configuring Devices and I/O Mapping ”, ⮫ “Linking a device input with an existing project variable ("mapping") ”, ⮫ “Mapping a device input to a recently created project variable ”, ⮫ “Linking a device with a function block instance ”, ⮫ “Changing and fixing an address value in the I/O map ”, ⮫ “Configuration of the I/O variable update ”, ⮫ “Monitoring of variables in the I/O map in online mode ”, ⮫ “Generating implicit variables for the forcing of I/Os ”, ⮫ “I/O mapping in one dialog for multiple devices ” ⮫ “AT Declaration ” ⮫ “Addresses ”
`‎<data type>‎`	Data Type `‎<elementary data type>‎` `‎<user defined data type>‎` `‎<function block >‎`	⮫ “Data Types ”, ⮫ Further information ⮫ “Object: DUT ” ⮫ “Object: Function Block ”
`‎<initial value>‎`	Initial Value `‎<literal value> \| <identifier> \| <expression>‎`	⮫ “Identifier Designation ”, ⮫ Further information ⮫ Constants and literals, ⮫ Constants and literals, ⮫ Constants and literals, ⮫ Constants and literals ⮫ “ST Expressions ”
`‎( ... )?‎`	Optional
`‎( ... )*‎`	Optional repetition

Example

‎GVL‎

{attribute 'qualified_only'}
{attribute 'linkalways'}
VAR_GLOBAL CONSTANT
        g_ciMAX_A : INT := 100;
        g_ciSPECIAL : INT := g_ciMAX_A - 10;
END_VAR

‎GVL_CONFIG‎

{attribute 'qualified_only'}
VAR_CONFIG
        // Generated instance path of variable at incomplete address
        PLC_PRG.fbDoItNow.XLOCINPUT AT %I*: BOOL := TRUE;
END_VAR

‎FB_DoIt (FB)‎

METHOD METH_Last : INT
VAR_INPUT
  iVar : INT;
END_VAR
VAR_INST
  iLast : INT := 0;
END_VAR

METH_Last := iLast;
iLast := iVar;

FUNCTION_BLOCK FB_DoIt
VAR_INPUT
    wInput AT %IW0 : WORD; (* Input variable *)
END_VAR
VAR_OUTPUT
    wOutput AT %QW0 : WORD; (* Output variable *)
END_VAR
VAR_IN_OUT
    aData_A : ARRAY[0..1] OF DATA_A; // Formal variable
END_VAR
VAR_EXTERNAL
        GVL.g_ciMAX_A : INT; // Declared in object GVL
END_VAR
VAR_STAT
    iNumberFBCalls : INT;
END_VAR
VAR
        iCounter: INT;
        xLocInput AT %I* : BOOL := TRUE; // VAR_CONFIG
END_VAR

iNumberFBCalls := iNumberFBCalls + 1;

‎PLC_PRG (PRG)‎

PROGRAM PLC_PRG
VAR
        iLoop: INT;
        iTest: INT;
        fbDoItNow : FB_DoIt;
        iTest_200: INT;
        aData_Now : ARRAY[0..1] OF DATA_A := [(iA_1 := 1, iA_2 := 10, dwA_3 := 16#00FF),(iA_1 := 2, iA_2 := 20, dwA_3 := 16#FF00)];
END_VAR

iTest := GVL.g_ciMAX_A;
iTest_200 :=  2 * GVL.g_ciMAX_A;
fbDoItNow(aData_A := aData_Now);
FOR iLoop := 0 TO GVL.g_ciSPECIAL DO
        ;
END_FOR

Variable initialization