{"id":325,"date":"2016-09-01T01:37:04","date_gmt":"2016-08-31T23:37:04","guid":{"rendered":"http:\/\/www.embedded-communication.com\/?p=325"},"modified":"2019-10-01T16:48:34","modified_gmt":"2019-10-01T14:48:34","slug":"ethercat-distributed-clocks","status":"publish","type":"post","link":"http:\/\/www.embedded-communication.com\/en\/ethercat\/ethercat-distributed-clocks\/","title":{"rendered":"EtherCAT Distributed Clocks"},"content":{"rendered":"

<\/p>\n

\"EtherCAT<\/h3>\n

What are Distributed Clocks?<\/h2>\n

\nEtherCAT uses Distributed Clocks<\/em> (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<\/em>. 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.<\/p>\n

<\/p>\n

Run time measurement<\/strong><\/h2>\n

Both the slaves as well as the cable cause a short delay of the telegrams on the network. To get a precise synchronization it is required to measure these delays and to take them into account. The master sends during the start-up phase a certain frame to determine the delays. Each slave writes the point of time of the reception of the frame into the frame – in both ways. Based on these timings the master is able to calculate the delays between each slaves.\n<\/p>\n

In addition to the Reference Clock<\/em> there is also a Master Clock<\/em> which contains the real time. This clock can be used to adjust the Reference Clock<\/em> at startup or later.<\/p>\n

Thus the following effects can be compensated:<\/p>\n