Skip to main content

Logical Operators

Logical (Boolean) operators are used to combine or invert conditions that evaluate to TRUE or FALSE. They’re essential for writing expressive, multi-condition IF statements.

Boolean Operations​

OperatorDescriptionExample
ANDTrue if both are trueA AND B
ORTrue if either is trueA OR B
NOTInverts a Boolean valueNOT A

Operator Use in IF Statements​

Logical operators are typically used inside IF conditions to control flow based on multiple inputs or states.

Example 1: Basic AND condition​


IF Start_Button AND NOT Stop_Button THEN
    Motor_Run := 1;
END_IF;

This will start the motor only if the start button is pressed and the stop button is not pressed.

Example 2: Using OR​


IF Emergency_Stop OR Fault THEN
    System_Enabled := 0;
END_IF;

This disables the system if either the emergency stop or a fault is active.

Example 3: Multiple combined conditions​


IF (Level < 50) AND (Pump_Enabled OR Manual_Override) THEN
    Pump := 1;
END_IF;

This turns on the pump if the level is low and either the pump is enabled or overridden manually.

Notes​

  • Parentheses can be used to group logic for clarity and precedence.

  • Avoid long, complex IF conditions without parentheses — they can become hard to read and debug.

Best Practices​

  • Keep Boolean expressions readable and explicit.

  • Use descriptive variable names so conditions make sense on their own.

  • Use NOT carefully — it only applies to the next expression, so grouping with parentheses is often safer.