Watchdog Alarm
medium
Raises an alarm if a heartbeat rising edge is not detected within the timeout period.
What it teaches
Timer reset by an external pulse (the heartbeat). If the timer reaches preset before the next pulse, the watchdog fires. Teaches retriggerable-timer semantics and the canonical "missing-pulse alarm" pattern used in comms and equipment health monitoring.
Parameters
| Tag | Direction | Type | Default | Description |
|---|---|---|---|---|
| In_Heartbeat | Input | BOOL | 0 | Heartbeat signal to monitor |
| Cfg_Timeout | Input | DINT | 1000 | Watchdog timeout in milliseconds |
| Sts_Alarm | Output | BOOL | 0 | 1 when the heartbeat is lost, 0 when active |
Required behavior
- The internal timer resets whenever In_Heartbeat transitions from 0 to 1.
- If the time since the last In_Heartbeat rising edge reaches Cfg_Timeout, Sts_Alarm becomes 1.
- Sts_Alarm clears to 0 as soon as a new In_Heartbeat rising edge is detected.