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PLCOPEN-N3: Define the names to avoid

Variable names must not collide with IEC 61131-3 keywords or standard library identifiers.

Why is it bad?​

Naming a variable TON, TOF, REAL, BOOL or any other reserved word shadows the standard library and confuses every reader of the code — including syntax-highlighting editors that will colour the variable as a keyword. Some parsers will even reject the program; others will silently bind the identifier to the user's variable, breaking any standard library function that the same POU also wants to call.

This rule walks every variable declaration and rejects names that match an IEC 61131-3 reserved word.

Example​

PROGRAM program0
  VAR
    TOF : INT;     (* PLCOPEN-N3 — collides with the off-delay timer *)
  END_VAR
END_PROGRAM

Use instead:

PROGRAM program0
  VAR
    timeout_off : INT;
  END_VAR
END_PROGRAM

Resources​

  1. PLCOpen Software Construction Guidelines