Optional Distributed Clocks Support; Fig. 13 Dc Tab For Indicating The Distributed Clocks Function; Fig. 14 Advanced Distributed Clocks Settings In The Ethercat Master - Beckhoff EK18 Series Documentation

Product overview
4.2.3

Optional distributed clocks support

Basic principles Distributed Clocks (DC)
The EtherCAT Distributed Clocks system comprises local clocks that are integrated in the EtherCAT slaves
and are synchronized by the EtherCAT master via special datagrams. Not all EtherCAT slaves support the
Distributed Clocks procedure. It is only supported by slaves whose function requires it. In the TwinCAT
System Manager a slave indicates its DC capability by showing "DC" in the settings dialog.
Fig. 13: DC tab for indicating the Distributed Clocks function
Once of these local clocks is the reference clock, based on which all other clocks are synchronized. See also
explanatory notes in the Basic EtherCAT documentation. The reference clock must be the first DC-capable
EtherCAT slave. By default TwinCAT therefore selects the first DC-capable device as reference clock. This is
shown (and can be modified by the user) under advanced properties of the EtherCAT master. The standard
setting should not be changed, except in cases where external synchronization is recommended in the
relevant documentation, for example.
Fig. 14: Advanced Distributed Clocks settings in the EtherCAT master
Fig. Advanced distributed clocks settings in the EtherCAT master illustrates how TwinCAT selects the
EL1252 as reference clock by default, since the preceding components do not support DC.
Settings EtherCAT device
System and infrastructure devices such as EK1100 or EK1122 couplers and junction etc. do not require
Distributed Clocks to function properly. Nevertheless, it may be topologically expedient to designate the first
coupler in an EtherCAT system as reference clock, for example. For this reason, from a certain level the
infrastructure components are able to operate as reference clocks, based on special configuration settings.
The components support activation of Distributed Clocks, based on the following table:
22 Version: 2.2 EK18xx