The functional principle of the TwinCAT EAP Configurator

All configuration parameters of a TwinCAT EAP device are organized by means of an object dictionary. This EAP object dictionary is structured in the same way as a CANopen object dictionary. The structure for a CANopen object dictionary is referred to by the CiA organization (CiA = CAN in Automation) as a profile. The profile for the EAP object dictionary was defined by the EtherCAT Technology Group (ETG) in the specification for the EtherCAT Automation Protocol (ETG 1005). The profile contains definitions for various objects. Each object is assigned a unique 16-bit index. An object can have up to 255 subentries. A data type must be defined for each subentry.

The TwinCAT EAP Configurator can read the objects of the EAP object dictionary from an EAP device and interpret them based on the EAP profile specification. In this way the EAP Configurator is able to display the communication links between all read EAP devices. If the configuration of an EAP device is changed, the content of the read objects is modified, deleted, or additional objects are created. The modified set of objects can then be re-written to the respective TwinCAT EAP devices, so that the modifications are applied.

By default, the TwinCAT EAP Configurator communicates with a TwinCAT EAP device via the ADS/AMS protocol during reading and writing of objects. ADS stands for Automation Device Specification. It describes a device- and fieldbus-independent interface. AMS stands for Automation Message Specification. It enables addressing of central and local systems such as PCs, and also Bus Controllers. ADS/AMS was specified by Beckhoff and is supported by the TwinCAT router. Messages that are sent in a network beyond the computer boundaries are transferred via TCP/IP. Therefore, the TwinCAT EAP Configurator can communicate via ADS/AMS both with a TwinCAT EAP device, which exist locally on the same PC, and with a TwinCAT EAP device that runs on another PC, which is integrated in the network.

Alternatively, the TwinCAT EAP Configurator can use the AoE protocol (AoE = ADS over EtherCAT) for reading and writing objects. The IP and UDP protocols are used for relaying and transporting the AoE messages. On this basis, each device within the network can be reached via an IP address. The specification of the AoE protocol can be found in the EtherCAT Protocol Enhancements (ETG 1020).

The difference between ADS/AMS communication and AoE communication is that, in contrast to ADS/AMS communication, AoE communication requires no TwinCAT router. The AoE protocol is one of the protocols that are classified as mailbox communication in TwinCAT.

The functional principle of the TwinCAT EAP Configurator 1:

Note the system configuration!

If the TwinCAT EAP Configurator and the TwinCAT EAP device run on the same computer, the communication between these two components only works via the ADS/AMS protocol. TwinCAT EAP devices running on another computer can also be reached via the AoE protocol.

TwinCAT processes both protocols acyclically. Their sole purpose is transfer of configuration data from or to the EAP device. Only the process data of EAP devices are processed and transferred cyclically and highly deterministically. The configuration of an EAP device defines the structure, size and transmission type of the process data.