Back to FBD referenceTypical FBD symbol for R_TRIG
Edges
R_TRIG
Rising-edge detector
The R_TRIG block compares the current IN value with the previous scan and emits a one-scan pulse on a rising edge.
Typical FBD symbol
IN
R_TRIG
Q
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| IN | BOOL | Yes | Signal whose rising edge is detected. |
Outputs
| Name | Type | Required | Description |
|---|---|---|---|
| Q | BOOL | Yes | TRUE only on the FALSE -> TRUE scan. |
Stateful
Yes, the block keeps internal state between scans.
Behavior rule
Q = TRUE for one scan when IN changes from FALSE to TRUE.
Scan table
Rising-edge example.
| Scan | IN | previous IN | Q |
|---|---|---|---|
| 1 | FALSE | FALSE | FALSE |
| 2 | TRUE | FALSE | TRUE |
| 3 | TRUE | TRUE | FALSE |
| 4 | FALSE | TRUE | FALSE |
Practical use
- count one button press;
- start a one-shot action;
- pulse a counter input.
What to watch
- Expecting Q to stay TRUE while IN is TRUE. R_TRIG emits one scan only.