Beckhoff EtherCAT EK112 Series Manual page 92

Basics
Fig. 69: 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. 70: Advanced Distributed Clocks settings in the EtherCAT master
The figure shows 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.
According to the following table (DC support from rev/firmware version), the components support activation
of distributed clocks:
92 Version: 3.6 EK112x, EK15xx