Functioning
All processes in the EL2252 are controlled by the SYNC0 pulse of the EtherCAT slave controller (ESC). In this EL2252 the ESC is a special IC that handles the EtherCAT communication. In contrast to many other applications, in the EL2252 the SYNC0 signal is not used cyclically free-running, but the process of writing data to the outputs is triggered when it occurs for the first time. To this end the user specifies (via the process data) the start time of SYNC0 and the required output states in which the EL2252 is written to and activated.
The ESC features an integrated local clock (distributed clock) that is continuously synchronized system-wide by the EtherCAT master with the master itself and with all other distributed clocks in the EtherCAT strand with a relative tolerance of < 100 ns.
The ESC in the EL2252 continuously and independently compares the start time with the current local distributed clock time. If the times match it immediately triggers the SYNC0 signal, which in turn internally leads to writing of the required output states.
When fully configured the distributed clock time is a 64 bit value with a resolution of 1 ns and a start time of 1.1.2000, 00:00 hours. When the EtherCAT strand starts up the EtherCAT master takes the time from the local PC and transfers it to the EtherCAT distributed clock network.
 | EtherCAT and Distributed Clocks A basic introduction to the subject of EtherCAT and Distributed Clocks can be downloaded from the Beckhoff website: |