Attention

IronPLC implements many parts of the IEC 61131-3 standard and is working toward full Structured Text support. Key features still missing include arrays and structures. Try it out in the IronPLC Playground.

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