STOBER
10 | More about MC6 and AS6?
05/2018 | ID 442461.04
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10.2.2.2
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 distributed 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. 25: 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 event for one synchronization is referred to as the Sync0 signal. Each slave generates it
own Sync0 signal cyclically using the respective SyncManager.
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.