EtherCAT

EtherCAT (Ethernet for Control Automation Technology) is a real-time Ethernet-based fieldbus protocol developed to meet the requirements of high speed, low latency, and precise synchronization in industrial automation systems. This protocol complies with the IEC 61158 standard and is widely used in motion control, data acquisition systems, and factory automation.

History

EtherCAT was developed in 2003 by the German company Beckhoff Automation and was established as an open standard in 2004 under the EtherCAT Technology Group (ETG). Today it is supported by more than 6000 member organizations worldwide.

Technical Architecture and Operation

Protocol Layers

EtherCAT uses the physical and data link layers of Ethernet but operates solely at Layer 2 by bypassing higher layers such as IP, TCP, and UDP. This enables significantly shorter cycle times and lower jitter.

Master-Slave Architecture

EtherCAT is configured with a single master and multiple slaves. Only the master device creates and transmits frames. The frame passes sequentially through all slave devices in the network. Each slave reads or writes its own data and forwards the frame to the next device. The data returns to the master at the end of the network.

On-the-Fly Processing

As the data frame passes through the slave devices, each device processes the data directly from the frame. This provides high bandwidth and low latency compared to conventional Ethernet protocols.

Frame Structure

EtherCAT frames are identified by a special EtherType field (0x88A4) embedded within the Ethernet header. Each frame contains one or more “datagrams.” These datagrams include information such as target address, command type (read/write), and operational data.

Synchronization

EtherCAT ensures that all devices in the network operate with microsecond-level synchronization using the “Distributed Clocks” mechanism. This feature is critical for multi-axis motion control applications.

Topology

EtherCAT can be configured in various topologies such as line, ring, star, or tree. This flexibility makes EtherCAT more adaptable and resilient to interruptions compared to conventional Ethernet networks. It also supports advanced topology features such as Hot Swap and redundancy.

Physical Layer and Hardware

EtherCAT operates with standard Ethernet hardware and cabling (e.g., CAT5, RJ45) and achieves full-duplex data transmission at 100 Mbps. Low-voltage differential signaling (LVDS) and fiber optic options are also available.

Error Detection and Security

EtherCAT uses cyclic redundancy check (CRC) and working counters on each slave device to ensure data integrity. This allows easy identification of fault sources in the network. It also includes pre-warning systems to detect potential frame corruption.

Application Areas

• Industrial automation
• Robotics systems
• CNC machines
• Automotive industry
• Real-time data acquisition and analysis systems
• Medical devices