Distributed Clocks

Distributed Clocks (DC)

In distributed clock mode the SSI communication is not started with the arrival of the EtherCAT frame, but through the slave's SYNC signal, which is synchronized via all DC-capable devices in the EtherCAT system. In this way a DC synchronization accuracy of 100 ns between devices can be achieved. Through further processing in the Box the actual start of the SSI communication achieves an accuracy of < ±500 ns relative to the ideal synchronous time.

Further information on the DC system can be found in the Basic EtherCAT documentation.

The minimum EtherCAT cycle time recommendations also apply in DC mode. If the Box is operated faster than the time required for SSI communication and processing, this is indicated through the SyncError status bit.

The DC mode is set under the DC tab and becomes active after a TwinCAT restart or reload.

• FreeRun: The module operates frame-triggered. Cyclic operation is started via the SyncManagers during EtherCAT frame processing.
• DC-Synchron: Cyclic operation in the module is started by the local distributed clock at exact intervals. The start time is chosen such that it coincides with other output slaves in the EtherCAT system.
• DC-Synchron (input based): as DC-Synchron mode, with the cyclic start time chosen such that it coincides with other input slaves in the EtherCAT system.