P4025¶

Code: P4025
Message: Bit access index is out of range for the variable type

This error occurs when a bit access index on a variable exceeds the number of bits available in the variable’s declared type.

Each integer and bit string type has a fixed number of bits:

SINT, USINT, BYTE: 8 bits (valid indices 0..7)
INT, UINT, WORD: 16 bits (valid indices 0..15)
DINT, UDINT, DWORD: 32 bits (valid indices 0..31)
LINT, ULINT, LWORD: 64 bits (valid indices 0..63)

Example¶

The following code will generate error P4025:

FUNCTION_BLOCK FB1
    VAR
        myByte : BYTE;
        myBool : BOOL;
    END_VAR

    myBool := myByte.8;  (* Error: BYTE has only 8 bits, valid range is 0..7 *)
END_FUNCTION_BLOCK

The variable myByte is declared as BYTE which has 8 bits (indices 0 through 7). Accessing bit 8 is out of range.

To fix this error, use an index within the valid range or use a wider type:

FUNCTION_BLOCK FB1
    VAR
        myWord : WORD;
        myBool : BOOL;
    END_VAR

    myBool := myWord.8;  (* Correct: WORD has 16 bits, valid range is 0..15 *)
END_FUNCTION_BLOCK