EtherCAT (Ethernet for Control Automation Technology)
Origins
EtherCAT was developed by Beckhoff Automation and first presented in 2003 at the Hanover trade fair. The goal: to create an industrial fieldbus offering extreme real-time performance while using standard Ethernet cabling and frames.
In 2003, the EtherCAT Technology Group (ETG) was founded to promote and standardize the technology. With over 7,000 members in 72 countries, it is today the largest fieldbus user group in the world. EtherCAT is standardized under IEC 61158 and IEC 61784.
Operating principle: "Processing on the fly"
EtherCAT's revolutionary concept is on-the-fly processing. Unlike conventional Ethernet networks where each node receives, processes, and then retransmits a frame, in EtherCAT:
- The master sends a single Ethernet frame that passes through all slaves in sequence.
- Each slave reads the data intended for it and inserts its own data as the frame passes through, without storing or retransmitting it.
- The frame returns to the master with all the collected data.
The delay added by each slave is about 1 microsecond. A network with 1,000 distributed I/O points can thus be refreshed in 30 microseconds, and a system with 100 synchronized servo drives in just 100 microseconds.
Technical specifications
| Physical bit rate | 100 Mbit/s (Fast Ethernet) — the full bandwidth is used |
| Cycle time | < 100 µs for hundreds of I/Os, < 30 µs for 1,000 digital I/Os |
| Topology | Line, tree, star, or combination — automatic detection |
| Number of nodes | Up to 65,535 slaves per segment |
| Distance | 100 m between two nodes (copper cable), more with fiber optic |
| Distributed clocks | Synchronization < 1 µs between all nodes (Distributed Clocks) |
| Compatibility | Standard IEEE 802.3 Ethernet frames — passes through standard Ethernet switches |
Protocols over EtherCAT
EtherCAT supports numerous application profiles encapsulated within its frames:
- CoE (CANopen over EtherCAT) — the most widely used profile, reusing the object model and SDO/PDO protocol from CANopen, easing migration from existing CAN networks.
- SoE (SERCOS over EtherCAT) — a profile optimized for motion control (servo drives).
- EoE (Ethernet over EtherCAT) — a tunnel for standard TCP/IP protocols over the EtherCAT network.
- FoE (File Access over EtherCAT) — file transfer for updating slave firmware.
Fields of application
- Industrial automation — control of production lines, assembly, packaging.
- Motion control — robotics, CNC machines, synchronized multi-axis systems.
- Metrology and testing — high-speed data acquisition, test benches.
- Semiconductors — lithography machines, wafer inspection.
- Wind energy — blade pitch control, turbine supervision.
EtherCAT vs CAN
| Criterion | CAN | EtherCAT |
|---|---|---|
| Bit rate | 1 Mbit/s | 100 Mbit/s (usable bit rate > 90%) |
| Latency | ~1 ms | < 100 µs |
| Max. nodes | ~127 | 65 535 |
| Domain | Automotive, embedded | Industrial automation |
| Gateway | CoE enables seamless CAN → EtherCAT migration | |
