Back to FBD referenceTypical FBD symbol for OR
Basic logic
OR
Logical OR
The OR block combines alternative conditions. Q becomes TRUE when IN1, IN2, or both inputs are active.
Typical FBD symbol
IN1
IN2
OR
Q
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| IN1 | BOOL | Yes | The first boolean condition. |
| IN2 | BOOL | Yes | The second boolean condition. |
Outputs
| Name | Type | Required | Description |
|---|---|---|---|
| Q | BOOL | Yes | The logical OR result. |
Stateful
No, the block does not keep internal state.
Behavior rule
Q = IN1 OR IN2
Truth table
| IN1 | IN2 | Q |
|---|---|---|
| FALSE | FALSE | FALSE |
| FALSE | TRUE | TRUE |
| TRUE | FALSE | TRUE |
| TRUE | TRUE | TRUE |
Practical use
- start from either of two pushbuttons;
- alarm from any active condition.
What to watch
- Using OR where all conditions must be true. Use AND for that case.