EC-EAP Stack: System-wide communication with the EtherCAT Automation Protocol (EAP)
The EtherCAT Automation Protocol (EAP) defines interfaces and services for an equal exchange of information between controllers (master/master communication) or for interfacing with a central master computer. The cyclic EAP communication can be handled directly in the user data of an Ethernet telegram, without the need for an additional transport or backup protocol. The EAP therefore enables very efficient data exchange without significant protocol overhead, with cycle times down to one millisecond or even faster. EAP is the preferred choice to implement a fast controller to controller communication. The protocol can used on any system equipped with a Standard Ethernet Controller. The lean protocol is suitable for high performance PCs as well as for low power ARM controllers.
The EC-EAP Stack requires just a conventional Ethernet interface for the communication. In conjunction with the high performance EC-Master Link Layers, a lot of variables could be transferred at a low system load.
Cyclic Process Data Exchange
The cyclic data exchange is based on the “pushed” or “polled” principle. In “pushed” mode, each communication device (publisher) sends its data cyclically or in a multiple of its own cycle. The receiver (subscriber) can be configured to specify which data should be received from which sender. As usual with EtherCAT, the sender and recipient data are configured via an object directory and process data mapping.
In the engineering environment of the Beckhoff TwinCAT system, the EtherCAT Automation Protocol is configured as an I/O device. With the EAP configurator the communication between all EAP devices could be defined, e.g. editing variables and setting update rates. For each EAP device the result is stored in a corresponding EAP Device Configuration (EDC) file. The EC-EAP stack initialize all internal variables, object and frames by evaluating this EDC file and is able to start communicating afterwards.
Further information about the EtherCAT Automation Protocol you will find on the EtherCAT Technology Group website.
EtherCAT Automation Protocol (EAP) Introduction