Variable Declaration

Variable declaration: Where and how?

You can declare variables at the following locations:

Declaration part of a POU
The Auto Declare dialog helps you with this.
Variable lists (GVL editor, NVL editor)
I/O mapping configuration of an I/O device object
For more information, see: Configuring Devices and I/O Mapping

For more information, see: Shortcuts for Variable Declaration

Syntax

<pragma>

<scope> <type qualifier>

<identifier> AT <address> : <data type> := <initial value> ;

END_VAR

`<pragma>`	Repeated optional (never, once, or multiple times) Pragma A pragma is a compiler statement (for example to achieve optimizations such as memory requirements or runtime improvements).	Using Pragmas Pragmas
`<scope>`	Required 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`	VAR VAR_CONFIG VAR_EXTERNAL VAR_GLOBAL GVL VAR_INPUT VAR_INST VAR_IN_OUT VAR_OUTPUT VAR_STAT VAR_TEMP
`<type qualifier>`	Optional Type qualifier `CONSTANT` `RETAIN` `PERSISTENT`	CONSTANT `RETAIN` PERSISTENT
`<identifier>`	Required Identifier, variable name Note: The rules listed in the chapter "Identifier Designation" have to be followed without exception when assigning an identifier. In addition, you will find recommendations for uniform naming.	Identifier Designation
`AT %<address>`	Optional The address is made up as follows: <memory area> <optional size prefix> <memory position> The memory area is subdivided into input memory area, output memory area, or flag memory area (`I`, `Q` or `M`). Example `AT %I* // Incomplete address` `AT %I7.5` `AT %IW0` `AT %QX7.5` `AT %MD48`	Configuring Devices and I/O Mapping AT Declaration Addresses
`<data type>`	Required Data Type Elementary data type Custom Data Type Function Block	Data Types DUT Function block
`<initial value>`	Optional Initial value; initialization as a literal, variable, or expression	Constants and literals ST Expressions

Example 12. Example

Global variable list GVL

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

Configuration variables 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

Function block FB_DoIt

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;

IEC program PLC_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