What are Distributed Clocks?
EtherCAT uses Distributed Clocks (DC) to synchronize the timing of the slaves. To achieve this each slave needs its own local time which is provided by an local clock source. The first DC-capable slave in the network is usually used as Reference Clock. All other slave synchronize their clock based on this reference clock. To handle it the EtherCAT master regularly send a telegram which is filled with the time of the reference clock and it is read by all other slaves.