Logical Operators

Logical operators combine or invert BOOL expressions that evaluate to 1 or 0. They are essential for writing expressive, multi-condition IF statements.

Operators

Operator	Description	Example
AND	1 when both operands are 1, else 0	A AND B
OR	1 when either operand is 1, else 0	A OR B
NOT	Inverts a BOOL — 1 becomes 0 and vice versa	NOT 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 BOOL 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.