What is EtherCAT?

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19 Jan 2024

What is EtherCAT?

Developed at Xerox's Palo Alto Research Center (PARC) in the 1970s, Ethernet was designed as a low-cost and fault-tolerant network interface for both local and wide area networks. At the time of its invention, other networks existed such as TokenBus, TokenRing, ARCNET, CDDI, and various lesser-known or proprietary network interfaces. There is no need to explain how Ethernet is changing industrial automation, but today we will talk about an increasingly widespread technology, EtherCAT.

EtherCAT was originally developed by Beckhoff Automation, a manufacturer of PLCs (Programmable Logic Controllers) used in industrial automation and real-time control systems. To solve the bandwidth problem of other interfaces, it developed its own version of Fieldbus called “LightBus” in the late 1980s. Subsequent additional work on this protocol eventually resulted in the invention of EtherCAT.

Introduced in 2003, EtherCAT is standardized under IEC 61158. Today, it is the fastest growing Fieldbus standard in the world.

Why was EtherCAT needed?

Why can't we just use ethernet to connect the DAQ and control systems? Ethernet is fast. It is cheap. Most importantly, it is easy to implement on today's computer-based devices. So what's missing? If time and determinism are important in an automation or motion control system, Ethernet will not be sufficient. EtherCAT is based on the “on-the-fly ethernet” principle, which is an important factor for fast cycle times in industrial automation applications.

EtherCAT, by contrast, uses the same physical and data link layers as Ethernet, but the protocols are different. Ethernet, as mentioned earlier, can route data through many different nodes in a master/slave configuration, sending and receiving according to requests. EtherCAT is a fast and deterministic network and processes data using specialized hardware and software. It uses a full-duplex, master-slave configuration and accommodates any topology. It can process 1,000 I/O points in 30 microseconds and communicate with 100 servo axes in 100 microseconds. The axes receive setting values and control data and report the actual position and status. The axes are synchronized using a distributed clock technique, which is a simple version of IEEE 1588 and reduces jitter to less than 1 microsecond.

The EtherCAT protocol provides fast transfer because messages are processed in hardware before being transmitted to the next slave. Slaves read data about themselves as the data frame passes and instantly add new data to the same data stream. This does not depend on the runtime of the protocol stack, so processing latencies are typically only a few nanoseconds.

In summary, EtherCAT is becoming increasingly common in control and motion applications with its low system cost, flexible topology, maximum performance, easy configuration, ability to communicate with existing industrial communication systems, safety features, and superior diagnostic features.