====== Understanding EtherCAT ======
===== Synchronisation and Timing =====
=== Official Documentation ===
[[https://infosys.beckhoff.com/english.php?content=../content/1033/ethercatsystem/2469122443.html&id=]]

=== Distributed Clock (DC) ===
The DC is an option on some slaves.
The Class B EtherCAT stack of Acontis does not suport DCs, but the Class A addon does ("//Synchronous with SYNC event//").
DCs allow synchronized reading of inputs and synchronized setting of outputs in the nanosecond range.

[[embedded_systems:ethercat:understanding_ethercat:Understanding_Sync_With_DC|Understanding synchronisation with DC]]

=== Synchronous with SM event ===
Without DC a synchronization of approximately some 10 to 100 microseconds is possible ("//Synchronous with SM event//").

=== Free Run ===
In "//Free Run//" mode the slave measures as fast as it can. However, the time interval between two measured values is not always the same and can easily change by a factor of two.


===== ENI and ESI files =====
==== ESI ====
  * EtherCAT Slave Information
  * Describes the slave. Every slave type has its own ESI file.
  * Can be downloaded from the manufacturer website
    * Maxon [[http://www.maxonmotor.ch/maxon/view/product/control/Positionierung/447293 |MAXPOS 50/5]] Downloads --> Handbücher --> English --> MAXPOS 50/5 ESI File (englisch, ZIP 48 KB)
    * Elmo:
      * Are installed with the 'EAS II' software from Elmo in ''Elmo Motion Control/Elmo Application Studio II/EtherCATSlaveLib''
      * Can be downloaded {{:embedded_systems:ethercat:esi.rar|here}}

==== ENI ====
  * EtherCAT Network Information
  * Describes the whole network. 
    * Which slave is connected, to which port from which other slave or master. 
    * Slave types
    * Cycle time
    * Which PDOs are transmitted in which order
  * Created with software EC-Engineer (one license is available at OST/Buchs-> Einar Nielsen)
    * {{:embedded_systems:ethercat:ec-master_quickstart_guide.pdf|EC-Master quickstart guide}} slide 8-16
    * After every change in the network (new slave or different connection sequence, different PDOs, different cycle time) the file has to be generated again.
    * An application which uses EtherCAT requres an eni-file for the current network