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02/2020 | ID 443025.06
9.5.2
DC-Sync: Synchronization using distributed clocks
Synchronization using the distributed clocks method allows the same time to be maintained for all nodes of an EtherCAT
network.
Each EtherCAT slave with distributed clocks functionality has a local clock. Normally, the time from the first DC-Sync-
capable EtherCAT slave downstream of the master in the network serves as the reference time. Both the master and the
slaves synchronize to this reference clock.
Reference
clock
Slave
clocks
Master
clock
Fig. 13: EtherCAT – Distributed clocks
The EtherCAT master automatically and continuously initiates the time coordination and synchronization.
At specified intervals, the EtherCAT master sends a frame into which the reference slave enters its current time. All other
slaves, as well as the master, read out this time from the circulating frame.
Because each slave experiences a certain delay when reading in the reference time due to the transmission path, the
respective run times between the reference clock and the slave clocks must be taken into account. This is why an individual
offset value is measured, calculated and parameterized for each slave.
The synchronous operation of all distributed master and slave clocks in the network allows for highly precise, relative time
information.
Moreover, this method has a high level of tolerance for fault-induced delays in the communication system thanks to the
clock distribution.
