Glossary · Industrial communication
Cyclic communication
Also known as: Cyclic data exchange, Periodic communication
German: Zyklische Kommunikation
In industrial communication, cyclic communication is the repeated exchange of the same set of data at a fixed interval, independent of whether the values have changed. It is used for process data such as inputs, outputs, setpoints and actual values.
- Industrial communication
In one sentence
Cyclic communication repeats the same process data at a fixed interval, giving controllers predictable update times.
Example
Every 2 ms, the motion controller sends new position setpoints to twelve servo drives and receives their actual positions in one EtherCAT cycle.
How it applies
- Engineering: Cyclic communication gives predictable timing, which control loops and synchronized motion need. The cycle time is chosen from the process requirements and limited by the number of devices and the data volume.
- Commissioning: Actual cycle times and Jitter are checked with the engineering tool or a network analyzer, especially after devices are added.
- Operation: If cyclic frames stop arriving, devices detect the loss with a watchdog and switch to a defined substitute behavior. That behavior must be configured deliberately; it isn't automatically safe.
- Documentation: The documentation team lists the cyclic data of a device (the I/O image with offsets, data types and units) and the supported cycle times, and describes the device's behavior when communication is lost.
Cyclic communication vs. polling
Polling means a client asks for data in its own rhythm, often over a non-deterministic network. Cyclic communication in fieldbuses is scheduled by the protocol itself, which gives defined update times. See also Acyclic communication.