Lenze EtherCAT Controller-based Automation - Manual (Page 19)

Lenze · Controller-based Automation · EtherCAT® Communication Manual · DMS 6.4 EN · 04/2014 · TD17
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4 The Lenze automation system with EtherCAT
4.1 Brief description of EtherCAT
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4.1.2 Communication
Compared with conventional Ethernet, the collision-free transfer of telegrams on the fieldbus
makes EtherCAT a real-time capable bus system.
Communication is always initiated by the EtherCAT master, i.e. the Lenze Controller. A telegram
sent by the master passes through all EtherCAT slaves. The last slave of the communication chain
sends the telegram back to the EtherCAT master. On the way back, the telegram is directly sent to
the EtherCAT master, without being processed in the slaves.
When EtherCAT is used, data are transferred in so-called "EtherCAT frames". The fieldbus nodes
only remove the data intended for them and do so while the EtherCAT frame is passing through the
device. Output data are inserted into the frame at the same time. Read and write access is always
carried out on a small section of the overall EtherCAT frame – the datagrams. This means that a
frame does not have to be received completely before it is processed. Each datagram is passed on
with minimal delay.