EtherCAT

What is EtherCAT?

EtherCAT (Ethernet for Control Automation Technology) is an open, real-time Industrial Ethernet protocol in which a single Ethernet frame travels past every device in a segment, and each device reads its own data from that frame and writes into it as it passes. Thanks to this processing “on the fly”, EtherCAT achieves cycle times of 100 µs or less and synchronises devices with a deviation well below one microsecond. That makes it a widely used network for motion control, fast I/O and machines with many servo axes.

The protocol was introduced by Beckhoff Automation in April 2003. The EtherCAT Technology Group (ETG) was founded in November 2003; it has managed the technology ever since and describes itself as the world’s largest industrial Ethernet and fieldbus organisation, with thousands of member companies.

🧠 What does EtherCAT do?

EtherCAT connects a controller, the MainDevice (formerly master), to actuators, sensors, I/O modules and drives, the SubDevices (formerly slaves). The ETG adopted these new terms a few years ago; you will see both in manuals and software.

The network is designed for:

• Motion Control - servo axes, robotics and CNC machines that must run in exact step
• Real-time I/O - hundreds to thousands of digital and analogue signals per cycle
• Synchronised processes - measuring, switching and moving at the same instant, to the microsecond
• Measurement systems - fast data acquisition at high sampling rates

🧱 How does EtherCAT work?

A conventional Ethernet network sends a separate packet to each device through a switch. EtherCAT works differently:

1. The MainDevice sends one frame - a standard IEEE 802.3 frame with EtherType 0x88A4. The MainDevice only needs an ordinary Ethernet port; no special interface card is required.
2. Each SubDevice processes the frame in hardware - an EtherCAT Slave Controller (ESC, an ASIC or FPGA) reads the output data addressed to it and writes its input data into the reserved area, adding only nanoseconds of delay.
3. The last device sends the frame back - over the return channel of the full-duplex link. Physically the network is a line; logically it is a ring.
4. The MainDevice checks the Working Counter - every device that processes its part increments this counter, so the controller knows in every cycle whether all data is consistent.

Because there is hardly any protocol overhead per device, EtherCAT uses more than 90% of the available bandwidth. A segment can hold up to 65,535 devices and uses a 4 GB logical address space. Where routing over IP networks is needed, the frame can also be encapsulated in UDP/IP.

Distributed Clocks (DC) take care of time synchronisation. The first DC-capable device acts as the reference clock; the MainDevice measures the propagation delay to every device and corrects the local clocks. In tests with 300 devices and 120 m of cable, jitter stayed well below 1 µs, which keeps latency predictable. The principle resembles the Precision Time Protocol, but is built directly into the EtherCAT hardware.

🔧 What are the key features of EtherCAT?

Alongside cyclic process data, EtherCAT has a mailbox for acyclic communication. It carries profiles such as CoE (CANopen over EtherCAT, using the object dictionary from CANopen), SoE (the servo drive profile from IEC 61800-7-204, known from SERCOS III), EoE (tunnelling Ethernet traffic through the segment), FoE (file transfer, for example for firmware) and AoE (ADS over EtherCAT). Every device also runs through a fixed state machine: Init, Pre-Operational (mailbox active), Safe-Operational (inputs valid, outputs in a safe state) and Operational, plus an optional Bootstrap state for firmware updates. For communication between controllers there is also the EtherCAT Automation Protocol (EAP), which can run over UDP/IP or TCP/IP as well.

🔄 How does EtherCAT compare with other protocols?

After PROFINET and EtherNet/IP, EtherCAT is the third most widely installed industrial Ethernet protocol in the world. It is chosen mainly for machines with many servo axes. Related real-time protocols are Powerlink and SERCOS III; for converged networks, TSN is gaining ground. For an overview of older technologies, see Fieldbuses.

🏭 Where is EtherCAT used?

• Packaging and food processing machines - many axes and I/O with short cycles
• Robotics - synchronised servos and axes in robot arms
• CNC machines - precise axis control and interpolation
• Semiconductor industry - thanks to SEMI E54.20, also in wafer handling and processing equipment
• Test and measurement systems - fast data acquisition with timestamps
• Assembly lines - real-time interaction between modules

Well-known MainDevice software is Beckhoff’s TwinCAT, which uses the standard Ethernet port of an industrial PC as the EtherCAT master. CODESYS, various soft PLCs and open-source stacks also support EtherCAT.

🛡️ How does functional safety work with EtherCAT?

Safety over EtherCAT (FSoE) carries safety data over the same network as standard data. FSoE uses the black channel principle: the safety container travels inside the process data, so the transport itself does not need to be safety-rated. FSoE was developed in line with IEC 61508, certified by TÜV Süd and standardised in IEC 61784-3-12. It is suitable for applications up to and including SIL 3, and TÜV-certified devices have been on the market since 2005.

The protocol alone does not make a machine safe. The machine builder determines the required Performance Level for each safety function according to ISO 13849 and demonstrates that the entire chain from sensor to actuator meets it. FSoE is comparable to PROFIsafe and CIP Safety on other networks. For more background, see functional safety.

🔐 How do you secure an EtherCAT network?

EtherCAT is not an IP protocol, and only the MainDevice may generate frames. That limits the attack surface of the segment itself. The ETG states that EtherCAT systems reach Security Level 2 of IEC 62443-3-3 without protocol changes, and SL 3 with software extensions, and refers to its ETG.1800 security profile. Even so, the frame itself carries no authentication: anyone with physical access to the segment can disrupt traffic.

The real risk usually lies with the MainDevice. That is often an industrial PC running Windows, engineering software and a network link to the plant network or the supplier. Practical measures:

1. Treat the MainDevice as the boundary - place it in its own zone and filter traffic to the business network through network segmentation.
2. Be sparing with EoE and EAP - tunnelling IP traffic through the segment or routing over UDP/IP opens extra paths; enable them only when needed.
3. Restrict physical access - close unused ports and secure the control cabinet.
4. Control remote maintenance - let supplier remote maintenance run through a controlled, logged connection.
5. Monitor the diagnostics - unexpected error counters or topology changes can point to faults as well as tampering.

🇪🇺 What does EtherCAT mean for Dutch and European machine builders?

In Dutch machine building, from packaging machines to high-tech equipment, EtherCAT combined with PC-based control is a common choice. Two European rules apply to new machines. The Machinery Regulation replaces the Machinery Directive from 20 January 2027 and requires protection against corruption of control systems. The Cyber Resilience Act sets requirements for products with digital elements, such as EtherCAT devices and control software. When buying a machine, ask about the security configuration of the MainDevice, the supplier’s update policy and documentation of the network layout.

❓ Frequently asked questions

What does EtherCAT stand for?

EtherCAT stands for Ethernet for Control Automation Technology. It is a real-time industrial Ethernet protocol that Beckhoff introduced in 2003 and that has since been managed by the EtherCAT Technology Group. The specification is laid down in IEC 61158 and IEC 61784-2.

Does EtherCAT require special hardware?

The EtherCAT MainDevice only needs a standard Ethernet port and software. Each SubDevice does contain an EtherCAT Slave Controller, an ASIC or FPGA that processes the frame in hardware. You do not use ordinary switches inside an EtherCAT segment; branches are made with EtherCAT junctions.

How fast is EtherCAT?

EtherCAT runs at 100 Mbit/s full duplex and uses more than 90% of that bandwidth. According to the ETG, EtherCAT updates 1,000 digital I/O points spread over 100 devices in about 30 µs and 100 servo axes in about 100 µs. EtherCAT G and G10 also allow 1 and 10 Gbit/s.

Is EtherCAT an open standard?

EtherCAT is an open technology: its specification is internationally standardised in IEC 61158, and membership of the EtherCAT Technology Group is open to anyone. Manufacturers test their devices with the official conformance test and at ETG interoperability events (plugfests).

What is the difference between EtherCAT and PROFINET?

EtherCAT passes a single frame through all devices and needs no switches, whereas PROFINET connects devices through switches and uses IRT with scheduled time slots for hard real-time. Both achieve synchronisation below one microsecond. In practice, the choice depends mainly on the PLC platform and the number of axes.

Is EtherCAT secure against cyber attacks?

EtherCAT uses no IP communication and only the MainDevice sends frames, which limits the attack surface. However, the EtherCAT frame itself has no authentication, and the MainDevice is often a PC connected to other networks. Protect that MainDevice in particular with segmentation, access control and limited use of EoE.

📌 In summary

EtherCAT is a real-time industrial Ethernet protocol in which one frame passes every device and each device processes its data in hardware, giving cycle times of 100 µs or less and synchronisation well below 1 µs. With Distributed Clocks, Safety over EtherCAT up to SIL 3 and standardisation in IEC 61158, it is an established choice for Motion Control, Robotics and demanding industrial automation. Secure the MainDevice above all, because that is where the EtherCAT segment meets the rest of the network.