P4083¶

Code: P4083
Message: Negated output assignment requires an output of type BOOL

This error occurs when a call negates an output that is not a BOOL. An output assignment written NOT q => v stores the inverse of the output q in v, and only a BOOL has an inverse in that sense: the assignment has no meaning for an INT, a TIME or any other type.

The compiler reports this error for an output of a function block, user-defined or standard (such as the ET output of a TON), of a function and of a method.

Example¶

The following code will generate error P4083:

Try it

Source

FUNCTION_BLOCK Limiter
  VAR_INPUT
    value : INT;
    limit : INT;
  END_VAR
  VAR_OUTPUT
    clipped : INT;
    over : BOOL;
  END_VAR
  over := value > limit;
  IF over THEN
    clipped := limit;
  ELSE
    clipped := value;
  END_IF;
END_FUNCTION_BLOCK

PROGRAM main
  VAR
    lim : Limiter;
    result : INT;
    ok : BOOL;
  END_VAR
  lim(value := 120, limit := 100, NOT clipped => ok);  (* Error: clipped is an INT *)
END_PROGRAM

clipped is an INT, so NOT clipped => ok has nothing to invert.

To fix this error, negate only a BOOL output, and assign any other output without NOT:

Try it

Source

FUNCTION_BLOCK Limiter
  VAR_INPUT
    value : INT;
    limit : INT;
  END_VAR
  VAR_OUTPUT
    clipped : INT;
    over : BOOL;
  END_VAR
  over := value > limit;
  IF over THEN
    clipped := limit;
  ELSE
    clipped := value;
  END_IF;
END_FUNCTION_BLOCK

PROGRAM main
  VAR
    lim : Limiter;
    result : INT;
    ok : BOOL;
  END_VAR
  lim(value := 120, limit := 100, clipped => result, NOT over => ok);
END_PROGRAM

Think IronPLC is wrong about this?

If you believe this diagnostic is incorrect, open an issue on GitHub with a small sample that demonstrates the problem.