EtherCAT Motion Bus Concepts

To exchange data between the controller (master) and the devices (slaves), the KAS Runtime relies on the EtherCAT motion bus. This communication is done in two modes: cyclic and non-cyclic (mailbox).

In cyclic mode, a single frame containing the data of all slaves (input and output) travels along all slaves and goes back to the master. Data is read and/or written on the fly by each slave.

The slave device input and output data definitions are:

• Outputs are written by the master and read by the slave device.
• Inputs are written by the slave device and read by the master.

EtherCAT Process Image

This cyclic frame is called the EtherCAT Process Image.

• It contains the Process Data, which is defined during network initialization.
• The cyclic data is grouped in predefined blocks called Process Data Objects or PDO.
• See these sections for more information about EtherCAT.
  • EtherCAT Functional Principle
  • EtherCAT Features
  • EtherCAT Implementation

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• PDOs contain real-time cyclic data which is deterministic.
  Non-cyclic data is not deterministic and is defined by Service Data Objects (ScDO).

References

• EtherCAT Specification V1.0 - see http://www.ethercat.org in the Member Area - Downloads.
• Büttner, H.; Janssen, D.; Rostan, M. (2003), EtherCAT - the Ethernet fieldbus, (PDF), PC Control Magazine 3: 14-19.

See Also