Communication state and communication alarms
Every driver reports two things continuously: that its process is alive, and how each of its devices communicates. From this YTCC marks signals as not connected, raises one communication alarm per device and shows the state on the home page and in system signals.
Device states
Each device of a driver is in one of four states:
| State | Meaning |
|---|---|
| Not connected | No connection to the device; after a delay this raises a communication alarm |
| Initial sync | The connection is up and the first full read (or general interrogation) is in progress; this is not a loss |
| Connected | The device communicates |
| Inactive | The device is switched off in the configuration; no alarm |
The usual sequence after a start or a reconnection is Not connected → Initial sync → Connected. A driver reports a change at once and otherwise repeats the state every 5 seconds.
Heartbeat of the driver
Each driver process sends a heartbeat every 2 seconds. If no heartbeat arrives for 6 seconds, the process counts as stopped: all its signals keep their last value but get the quality not connected, and a driver alarm is raised. The process manager restarts a stopped driver after 1, 2, 5 and 10 seconds and then every 30 seconds; see Common driver concepts.
Communication alarms
- One alarm per device. It is raised when the device stays not connected for 5 seconds without interruption. For a device that has not yet been seen connected since the alarm engine started, the first alarm waits 30 seconds, so a normal start does not raise alarms.
- One alarm per driver when its heartbeat stops (after 6 seconds) or never arrives (30 seconds after the start).
- The alarms have priority High, must be acknowledged and cannot be shelved. They return when the device or the driver communicates again.
- They count in Alarms.Summary only, not in areas or groups.
The alarm text names the device and the last error reported by the driver; see The alarm list.
Signal quality
The quality of a signal follows communication, not the age of its value: a value that does not change for hours stays good as long as the device communicates. When a device is lost, the driver sets its signals to not connected (for Modbus with Set invalid on disconnect, on by default); when the process stops, the server does it for all signals of the driver. See Quality.
Where you see the state
- Home page › Processes: the Communication column shows whether a driver communicates with at least one device; see Manage the stack.
- Alarm list: the communication alarms.
- System signals
System.Drivers.<driver>andSystem.Drivers.<driver>.<device>: running, number of devices and connected devices, the state of each device (0 to 3), frame counters, the last error and the device diagnostics; see System, alarm and session signals. - Configuration editor: the Communication diagnostics panel of a device in the Drivers view; see Add drivers and devices.
Good to know
- The texts of communication alarms are written by the server in the project's Operator language, for example "<name> communication lost — <reason>" and "<name> communication restored" in English. A change of the language applies after the project is restarted; alarms already recorded keep their language.