Using the EtherCAT Industrial Communication Protocol In Designs

1 of Enlarge image

Example of an EtherCAT network

EtherCAT Telegram format

Components of an EtherCAT node

Basic Digital I/O EtherCAT Device

EtherCAT with ASIC and external processor

Integrated EtherCAT with processor

EtherCAT Slave on Sitara AM335x micro

EtherCAT is among the leading communications standards based on Ethernet that is used increasingly for networking and communications in the industrial or factory environment for input/output (I/O) devices, sensors and programmable logic controllers (PLCs). It was invented by Beckhoff Automation in Germany and later standardized by the EtherCAT Technology Group (ETG), established to help with the proliferation of the EtherCAT standard. Today, there are more than 1,700 member companies from 52 countries that create and deploy EtherCAT-compatible products. To ensure broad interoperability among devices designed with EtherCAT interfaces, the EtherCAT Technology Group (ETG) has several rograms for ensuring compliance with the technical specifications.

Ethernet has seen unparalleled adoption in diverse applications, but in an industrial environment, it is still not efficient enough for small amounts of data exchange, it has low determinism for real-time operation, and it works with only star topology in which the network nodes must be connected through switches. EtherCAT technology adds certain features on Ethernet and enforces certain configurations to make it a very efficient network technology for automation while fully conforming to the Ethernet specifications.

The design of EtherCAT (Fig. 1) enables any standard PC to be used as an EtherCAT master and communicate with EtherCAT slaves, which are specialized devices compliant with EtherCAT specification. Together, the master and slave EtherCAT devices can be used in all devices in the factory network – automation controllers, operator interfaces, remote I/O units, sensors, actuators, drives and others. The EtherCAT standard supports any topology — line, star or tree — and the bus structures common in fieldbus networks can also be realized with EtherCAT. Since the EtherCAT interface is present on I/O devices, there is no requirement for any Ethernet switching hardware. With the 100m range of copper links and even longer with optical links, EtherCAT can span over thousands of devices spread across a large geographical area. For short distances, such as on back-plane, EtherCAT uses E-bus, a differential signaling technology.

EtherCAT improves upon traditional Ethernet by implementing “on-the-fly” processing where the nodes in EtherCAT network read the data from a frame as it passes through. All EtherCAT frames originate from the EtherCAT master which sends commands and data to the slaves. Any data to be sent back to master is written by the slave into the frame as it passes through. This helps eliminate the need for point-to-point exchange of small-sized frames between master and individual slaves and drastically improves the efficiency of communication. However, it also means that each slave must have two Ethernet ports and be able to let the frame pass through while reading from or writing to the passing frame and therefore, specialized hardware is required in the slave devices. As a result of these improvements, the usable bandwidth in a 100Mbps network running EtherCAT is more than 90 percent as compared to less than 5 percent for networks where the master must separately communicate with each slave node.