Index access to bits integer variables

You can address individual bits in integer variables. To do this, append the variable with a dot and the index of the addressed bit. The bit-index can be given by any constant. Indexing is 0-based.

Syntax

<integer variable name> . <index>
<integer data typ> = BYTE | WORD | DWORD | LWORD | SINT | USINT | INT | UINT | DINT | UDINT | LINT | ULINT

Example

In the program, the third bit of the variable ‎wA‎ is set to the value of variable ‎xB‎. The constant ‎c_usiENABLE‎ acts as an index to access the third bit of the variable ‎iX‎.

Index access

PROGRAM PLC_PRG
VAR
        wA : WORD := 16#FFFF;
        xB : BOOL := 0;
END_VAR

// Index access in an integer variable
wA.2 := xB;

Result: ‎wA = 2#1111_1111_1111_1011 = 16#FFFB‎

Constant as index

// GVL declaration
VAR_GLOBAL CONSTANT
        gc_usiENABLE : USINT := 2;
END_VAR

PROGRAM PLC_PRG
VAR
        iX : INT := 0;
END_VAR

// Constant as index
iX.gc_usiENABLE :=  TRUE;       // Third bit in iX is set TRUE

Result: ‎iX = 4‎