Selection of the process data
The process data transferred by an EtherCAT slave during each cycle (Process Data Objects, PDOs) are user data which the application expects to be updated cyclically or which are sent to the slave. To this end the EtherCAT master (Beckhoff TwinCAT) parameterizes each EtherCAT slave during the start-up phase to define which process data (size in bits/bytes, source location, transmission type) it wants to transfer to or from this slave. Incorrect configuration can prevent successful start-up of the slave.
For Beckhoff EtherCAT EL/ES/EP slaves the following applies in general:
- The input/output process data supported by the device are defined by the manufacturer in the ESI/XML description. The TwinCAT EtherCAT Master uses the ESI description to configure the slave correctly.
- The process data can be modified in the system manager. See the device documentation. Examples of modifications include: Mask out a channel, displaying additional cyclic information, 16-bit display instead of 8-bit data size, etc.
- In so-called “intelligent” EtherCAT devices the process data information is also stored in the CoE directory. Any changes in the CoE directory that lead to different PDO settings prevent successful startup of the slave. It is not advisable to deviate from the designated process data, because the device firmware (if available) is adapted to these PDO combinations.
Proceed as follows to activate or deactivate individual PDOs.
- 1. Select the device to be configured at Solution Explorer.
- 2. Open the "Process Data" tab.
- 3. Select Sync Manager "Inputs" or "Outputs".
- 4. Activate or deactivate the PDOs.
- The activated PDOs appear as variables in the tree structure below the device at the Solution Explorer.
- 5. Optionally select a "Predefined PDO Assignment". "Predefined PDO Assignments" are useful predefined assemblies of process data objects.
