EtherCAT-specific Properties - General Information on EtherCAT CoE
This topic contains the following sections:
| Note
Refer to the PLCnext Info Center for a list of controllers supporting EtherCAT. |
| Note
The EtherCAT application needs to be installed on PLCnext Technology controllers via the PLCnext Store. |
| Note
Preconditions for using EtherCAT The EtherCAT functionality and therefore also the EtherCAT-related PLANT nodes and editors are only available if the controller supports this (PLCnext Technology controllers from firmware version 2026.0) and the functionality has been activated in PLCnext Engineer. To do this, proceed as follows:
Furthermore, EtherCAT devices must be added to the COMPONENTS by importing the respective ESI files. Only after the ESI files have been imported are the devices available in the COMPONENTS (category 'Network | Local | Devices | ESIImport') and can be inserted in the station editor under the 'EtherCAT' node. |
Basics
EtherCAT is a real-time field bus system which is based on the Ethernet technology. It does not require any switches. Instead, I/O modules etc. can be directly connected and accessed via EtherCAT.
If supported by the EtherCAT master, up to 65,535 slave devices can be connected. Basically there are no restrictions regarding the bus topology: line, tree, star and ring topologies are possible (where a ring topology enables cable redundancy).
| Note
For controller specific quantities, refer to the PLCnext Store or PLCnext Info Center. |
PLCnext Technology supports the CAN-over-EtherCAT profile implemented by the CiA (CAN in Automation) organization. Through this profile (protocol), EtherCAT offers the same communication mechanisms as in the CANopen® standard (similar network management). This makes it possible to adapt the firmware of CANopen® devices accordingly and use them with EtherCAT.
EtherCAT uses standard Ethernet frames for communication. The EtherCAT user data is embedded in these frames. The frames are transmitted cyclically (configured in the EtherCAT master) through the network. Each participant connected to the EtherCAT network recognizes the data relevant for it and can read from and write data into the frame. This happens during runtime.
Process Data Objects Mapping
Process data is organized in so-called Process Data Objects (PDOs): A PDO may be a single process data item or a combination of several process data items belonging to one slave. PDOs distinguish between two data directions, i.e. Receive (RX) PDOs and Transmit (TX) PDOs, whereby the designation is made from the device perspective in each case: an input/output module sends its input data with TX PDOs and receives output data in RX PDOs.
With other fieldbuses the entire set of process data are transferred between master and slaves in each bus cycle, regardless of whether they are used in the application or not. With EtherCAT this is different: due to the selective PDO mapping, the transferred data volume per cycle can be limited to the actually needed process data.
After the required PDOs have been selected (activated) in PLCnext Engineer by the user, the master configures and maps these process data in the slaves during the EtherCAT startup. Due to the selective process data mapping different amounts of data can be exchanged per participant: from one bit information over some bytes up to kilobytes.
Implementation of slave data
As defined by the EtherCAT CoE protocol, the following data of each slave device are implemented and used:- Object Dictionary. In PLCnext Engineer visible in the 'CoE Data' editor.
- PDO (Process Data Objects). The CANopen over EtherCAT (CoE) protocol allows the user to map objects to PDOs in order to use the PDOs for realtime data transfer. The PDO mappings define which objects will be included in the PDOs.The 'PDO Data' editor allows selective mapping of process data. Selected PDOs are automatically inserted into the 'Data List' of the respective EtherCAT slave. In the Data List, they can be assigned to global PLC variables in your project and further processed in your application.
- SDO (Service Data Objects) are used to transfer device parameters and diagnostic information. They are not time-critical and are transmitted acyclically as so-called SDO frames. SDOs are exchanged via a separate memory area (than PDOs) called the mailbox.SDO (Service Data Objects) are currently not visible in PLCnext Engineer. Instead, they are used in the background to read the Object Dictionary and to provide diagnostic information to the available diagnostic tools.
- 'Init commands' list editor for each slave station.
- 'Distributed clock' editor for each slave station that supports the DC functionality.