EtherCAT Slave Module Tutorial - NI (2024)

In EtherCAT, data is sent as Service Data Objects (SDOs) or Process Data Objects (PDOs). SDOs are used for non-cyclic communication, which is typically configuration. PDOs are used for cyclically transferred data, such as I/O samples. The cRIO ECAT S module can automatically receive some SDO data, which is handled by the module’s onboard logic and is not user-configurable. Primary communication between the module and the EtherCAT network takes place using PDOs.

The cRIO ECAT module provides 1024 Bytes for both Tx and Rx PDOs. The PDO-Configurator, a standalone utility, allows you to set the data type (Bool, Int, UInt or Array), name, and direction of each PDO.

The PDO-Configurator will output two necessary files: the ESI file and a PDO file. The ESI file (EtherCAT Slave Information) is a standard file that each EtherCAT slave provides to identify itself and its communication structure. This file is saved in XML format and is sometimes referred to as “the XML file”. The PDO file is a custom binary file that contains information that needs to be sent to the cRIO ECAT S module to configure it to your desired PDO configuration.

The labels “RX” and “TX” represent Receive and Transmit and are from the perspective of the network. For example, a module TXPDO is a PDO that the cRIO ECAT module receives from the EtherCAT network. Determining if you need both RXPDOs and TXPDOs will require knowledge of your objectives for this EtherCAT device as a part of the larger network – what will the master send to it? What will it send to the master? These are core questions to determining the type and number of PDOs to create.

To create a PDO, go toPDOs»Add RxPDOorAdd TxPDObased on which you would like to create.

Figure 2.Creating a TxPDO in the PDO-Configurator

Once you create a PDO file, you’ll need to populate it with variables. For an RXPDO, these need to match the data being sent to this EtherCAT device (both in index and datatype). You can add variables by going toVariables»Add Var. Then, set the Variable Name and Data Type. If you change Number of Elements to something else, then one the configurator will create an array datatype. The Index of each variable will be important later when you wish to access PDO data in your LabVIEW application.
Note:The NI EtherCAT Master software does not support array data types.

Figure 3.Setting the data type of a RxPDO variable in the PDO-Configurator

The module is accessed and programmed through property and method nodes in LabVIEW FPGA. There are three methods and three properties for the module and sync methods for data exchange. The module methods are Reset, Update and Write PDO file. Reset must be used if the module becomes corrupted and goes into exception state. The Update method gives you control to initiate the SPI transfer between FPGA and module memory. You can either update the Tx or Rx or both memories. Keep in mind that each transfer takes time and if you use both memories you should always update them at the same time. The Write PDO file method allows you to update the PDO configuration as mentioned in theDownloading to Modulesection. The module properties are vendor ID, module ID and serial number and are characterizing the module. You might want to read those properties ones, to identify your module. At last the data exchange methods give access to the PDO and Sync data.

To see these methods in action, you can open one of the examples. The Getting started example uses most of the programing elements and the Getting started DC example uses all of them. It adds time synchronization to the Ethercat network. These examples can be found in the Example Finder viaLabVIEW»Help»Find Examples. Choose the directoryToolkits and Modules»Third-Party Add-Ons»KUNBUS GmbH»EtherCAT.

As mentioned underExporting Datathe ESI XML file and the PDO configuration uses a unique 8-digit ID. The first 4 digits are representing the unique module ID and the last 4-digits are representing the checksum for your specific PDO configuration. That way the NI EtherCAT Master who uses SDO communication to read the modules product code can differentiate between multiple modules in your network and multiple configurations for the same module.

To use an NI device as a master, you’ll first need to install NI-Industrial Communications for EtherCAT to both the development PC and the Real-Time controller. After this, you can add the slave to a LabVIEW project as outlined in the article:Adding Third-Party EtherCAT Slaves in LabVIEW.

The Getting started example brings the ECAT_RT_NI-Master Example VI, that uses the programmatic way of querying the EtherCAT network compared to the static project-based method. To use the example, the ESI XML file needs to be imported to your RT target that holds the module.

In case you want to store, remove or rename ESI files manually, here are the paths to both locations:

Note:If you change anything manually you need to restart the target or Host LabVIEW for the XML changes to be recognized.

If working with a third party master, consult their documentation on how to add a slave to the network. Many master software programs require the ESI file for the slave, which you created in “Configuring PDO Data”.