EtherCAT (Ethernet for Control Automation Technology) is an Ethernet-based fieldbus system developed by Beckhoff Automation. The protocol is standardized in IEC 61158 and is suitable for both hard and soft real-time computing requirements in automation technology.
The goal during development of EtherCAT was to apply Ethernet for automation applications requiring short data update times (also called cycle times; ≤ 100 μs) with low communication jitter (for precise synchronization purposes; ≤ 1 μs) and reduced hardware costs. Typical application fields for EtherCAT are machine controls (e.g. semiconductor tools, metal forming, packaging, injection molding, assembly systems, printing machines, robotics). Remote controlled hump yard facilities used in the railroad industry.
With EtherCAT, the standard Ethernet packet or frame (according to IEEE 802.3) is no longer received, interpreted, and copied as process data at every node. The EtherCAT slave devices read the data addressed to them while the telegram passes through the device, processing data "on the fly". In other words, real-time data and messages are prioritized over more general, less time-sensitive or heavy load data.
Similarly, input data are inserted while the telegram passes through. A frame is not completely received before being processed; instead processing starts as soon as possible. Sending is also conducted with a minimum delay of small bit times. Typically the entire network can be addressed with just one frame.[2]
*optional, the TCP/IP Stack shown is not needed for typical fieldbus devices. EtherCAT master can access all data including name and data types of an EtherCAT slave without complex tools. EtherCAT uses Standard Ethernet (IEEE 802.3 - Ethernet MAC and PHY) without modifications.
Protocol
The EtherCAT protocol is optimized for process data and is transported directly within the standard IEEE 802.3 Ethernet frame using Ethertype 0x88a4. It may consist of several sub-telegrams, each serving a particular memory area of the logical process images that can be up to 4gigabytes in size. The data sequence is independent of the physical order of the nodes in the network; addressing can be in any order. Broadcast, multicast and communication between slaves is possible, but must be initiated by the master device. If IP routing is required, the EtherCAT protocol can be inserted into UDP/IP datagrams. This also enables any control with Ethernet protocol stack to address EtherCAT systems.
Performance
Short cycle times can be achieved since the host microprocessors in the slave devices are not involved in the processing of the Ethernet packets to transfer the process images. All process data communication is handled in the slave controller hardware. Combined with the functional principle this makes EtherCAT a high performance distributed I/O system: Process data exchange with 1000 distributed digital I/O takes about 30 μs, which is typical for a transfer of 125 byte over 100Mbit/s Ethernet. Data for and from 100 servo axis can be updated with up to 10kHz. Typical network update rates are 1–30kHz, but EtherCAT can be used with slower cycle times, too, if the DMA load is too high.
The bandwidth utilization is maximized, as each node and each data do not require a separate frame. Thus, extremely short cycle times of ≤ 100 μs are achievable. By using the full-duplex features of 100BASE-TX, effective data rates of more than 100Mbit/s (> 90% user data rate of 2x100Mbit/s) can be achieved.
The EtherCAT technology principle is scalable and not bound to 100Mbit/s. EtherCAT G and 10G are new extensions of standard EtherCAT using 1gbps and 10gbps respectively for significantly increased bandwidth to meet the needs of IIoT and Industry 4.0
Topology
Using full-duplex Ethernet physical layers, the EtherCAT slave controllers close an open port automatically and return the Ethernet frame if no downstream device is detected. Slave devices may have one, two, or more ports. Due to these features EtherCAT enables a multitude of network topologies, including line, tree, ring, star, or any combination thereof. The protocol also enables a multitude of communication features such as cable redundancy, Hot Connect of segments, change of devices during operation, or even master redundancy with Hot Standby.
Thus the combination of the topology variations and different network architectures, e.g. sub-ordinated or neighboring control systems with consistent synchronization, enables numerous possibilities. Additional switches are not required. The physics of Ethernet allow a cable length of up to 100m (300ft) between two nodes, so the E-bus (LVDS) is only intended for use as the physical layer for modular devices. For each cable path, the signal variant can be chosen individually. For higher distances, or the complete galvanic isolation between two slaves, fiber optic cables are used. With single-mode fiber, distances up to 20km between two nodes can be bridged. Since a total of 65,535 nodes per network segment can be connected, the network extension is nearly unlimited.
Synchronization
For synchronization a distributed clock mechanism is applied, which leads to very low jitter, significantly less than 1 μs, even if the communication cycle jitters, which is equivalent to the IEEE 1588 Precision Time Protocol standard (PTP). Therefore, EtherCAT does not require special hardware in the master device and can be implemented in software on any standard Ethernet MAC, even without dedicated communication coprocessor.
The typical process of establishing a distributed clock is initiated by the master by sending a broadcast to all slaves to a certain address. Upon reception of this message, all slaves will latch the value of their internal clock twice, once when the message is received and once when it returns (remember EtherCAT has a ring topology). The master can then read all latched values and calculate the delay for each slave. This process can be repeated as many times as required to reduce jitter and average out values. Total delays are calculated for each slave depending on their position in the slave-ring and will be uploaded to an offset register. Finally the master issues a broadcast readwrite on the system clock, which will make the first slave the reference clock and forcing all other slaves to set their internal clock appropriately with the now known offset.
To keep the clocks synchronised after initialization, the master or slave must regularly send out the broadcast again to counter any effects of speed difference between the internal clocks of each slave. Each slave should adjust the speed of their internal clock or implement an internal correction mechanism whenever they have to adjust.
The system clock is specified as a 64 bit counter with a base unit of 1ns starting at January 1, 2000, 0:00.
Diagnosis
The fast, precise detection of disturbances is one of many diagnostic features of EtherCAT.
Bit errors during transmission are detected reliably by the analysis of the CRC check sum: the 32 bit CRC polynomial has a minimum Hamming distance of 4. Besides the error detection and localization protocol, the transmission physics and topology of the EtherCAT system allow individual quality monitoring of every single transmission path. The automated analysis of the according error counters enables the exact localization of critical network segments.
More info to follow in the chapter titled "Monitoring".
Device Profiles
The device profiles describe the application parameters and functional behavior of the devices, including device-specific state machines. The following software interfaces are provided for existing device profiles. Thus, the migration to EtherCAT by adjusting the firmware and the hardware is simplified significantly.
CAN application protocol over EtherCAT (CoE)
CANopen devices and application profiles are available for an extensive selection of device categories and applications: I/O modules, drives (e.g., drive profile CiA 402 standardized as IEC 61800-7-201/301), encoders (CiA 406), proportional valves, hydraulic controllers (CiA 408), or application profiles. In this case, EtherCAT replaces CAN.
Servodrive-Profile over EtherCAT (SoE)
SERCOS interface is a real-time communication interface, ideal for motion control applications. The SERCOS profile for servo drives and communication technology are standardized in IEC 61800-7. This standard also contains the mapping of the SERCOS servo drive profile to EtherCAT (IEC 61800-7-304).
Related protocols
Ethernet over EtherCAT (EoE)
Any Ethernet device can be connected within the EtherCAT segment via switch ports. The Ethernet frames are tunneled via the EtherCAT protocol, as is normal for internet protocols (e.g., TCP/IP, VPN, PPPoE (DSL), etc.). The EtherCAT network is fully transparent for the Ethernet devices, and the real-time features of EtherCAT are not disturbed.
Safety over EtherCAT (FSoE)
In parallel to the development of EtherCAT, a fieldbus-independent safety protocol has been developed.[3] For EtherCAT, it is available as "Safety over EtherCAT" (FSoE = Fail Safe over EtherCAT). With FSoE, functional safety with EtherCAT can be realized. The protocol as well as the implementation are certified by TÜV and meet the requirements of the Safety Integrity Level 3 according to IEC 61508. Since 2010, Safety over EtherCAT is internationally standardized to IEC 61784-3-12. EtherCAT provides a single-channel communication system for transferring safe and non-safe information. The transport medium is regarded as a black channel,[4] and thus is not included in safety considerations.
File over EtherCAT (FoE)
This simple protocol is similar to TFTP (Trivial File Transfer Protocol); it enables file access in a device and a uniform firmware upload to devices across an EtherCAT network. The protocol has been deliberately specified in a lean manner, so that it can be supported by boot loader programs. A TCP/IP stack isn’t required.
Monitoring
Since EtherCAT uses standard Ethernet frames according to IEEE 802.3, any standard Ethernet tool can be used to monitor the EtherCAT communication. Additionally, there is free-of-charge parser software for Wireshark (formerly Ethereal, an open source monitoring tool) and the Microsoft network monitor, with which recorded EtherCAT data traffic can be comfortably prepared and displayed.
Gateways
By using gateways, existing networks such as CANopen, DeviceNet, or Profibus, can be integrated into the EtherCAT environment seamlessly. Furthermore, gateways provide a trip-free migration path from a traditional fieldbus to EtherCAT, reducing further investment costs.
Thanks to the performance of EtherCAT, communication with external fieldbus masters is as fast as with traditional cards connected via PCI or other backbone buses. Since decentralized fieldbus interfaces lead to shorter extensions, they can be operated with even higher baud rates than would have been possible with the traditional architecture.
Implementation
EtherCAT Technology Group (ETG) encourages and expects companies that develop EtherCAT products to join ETG, so that they can get an EtherCAT Vendor-ID, get access to the full documentation, to the developers forum and to the slave stack code, that Beckhoff provides free of charge to ETG members.
Master
Masters can be implemented as a software solution on any Ethernet MAC. Different manufacturers provide code for different operating systems, including several open-source projects. Due to the relocated mapping on the slave hardware, demands are reduced for CPU performance of the master. The master already contains the data as a readily sorted process image.
In order to operate a network, the EtherCAT master requires the cyclic process data structure as well as boot-up commands for each slave device. These commands can be exported to an EtherCAT Network Information (ENI) file with the help of an EtherCAT configuration tool, which uses the EtherCAT Slave Information (ESI) files from the connected devices.[5]
Slave
EtherCAT microcontroller
Contrary to the operation of standard Ethernet, the slaves process the EtherCAT frames on the fly. This requires the use of hardware-integrated EtherCAT Slave Controllers (ESC) in the slaves. ESCs are also available as ASICs or based on FPGAs. Since the beginning of 2012, standard microprocessors with EtherCAT slave interfaces are also available.
For simple devices, no additional microcontroller is required. In more complex devices, however, the communication performance of EtherCAT is nearly independent of the performance of the used controller. Thus the requirements for the microcontroller are determined by the local application, e.g. the drive control.
There is a choice of development boards, both from the EtherCAT Slave Controller suppliers and from third party vendors. There are also open-source projects for EtherCAT slave device development boards, such as SOES and ArduCAT.
Control and regulation
For the control and regulation of physical processes, high data integrity, data security, and synchronicity is required. EtherCAT has been designed especially for these kinds of applications and meets all demands for fast controls.
Measurement systems
Modern measurement systems are characterized by multi-channeling, synchronicity, and accuracy. Due to the advanced protocol features of EtherCAT, efficient synchronous data throughput is assured. The network features based on Ethernet enable a measurement network with distributed measurement modules.
Organization
The EtherCAT Technology Group (ETG) was established in 2003, and is the industrial Ethernet user organization with the most members in the world today.[6][7] A wide range of industrial controls vendors, OEMs, machine builders, and technology organizations from around the world constitute the ETG member roster. The ETG offers its members implementation support and training, organizes interoperability tests (often called "Plug Fests"[8]), and promotes the development and distribution of the technology, supported by its members and the teams working in offices in Germany, China, Japan, Korea, and North America. ETG end users span numerous industries, with machine builders and suppliers of powerful control technology joining forces to support and promote EtherCAT technology. The variety of industries guarantees optimal preparation of EtherCAT for the widest range of applications.[9] System partners give qualified feedback for the simple integration of hardware and software modules in all required equipment classes. The EtherCAT Conformance Test Tool (CTT),[10] developed with the assistance of ETG member companies, ensures the interoperability and protocol conformity of EtherCAT devices.
Standardization
The EtherCAT Technology Group (ETG) is an official liaison partner of the IEC (International Electrotechnical Commission) working groups for digital communication. The EtherCAT specification was published as IEC/PAS 62407[11] in 2005, which was removed end of 2007 since EtherCAT had been integrated into the international fieldbus standards IEC 61158[12][13] and IEC 61784-2[14] as well as into the drive profile standard IEC 61800-7.[15] These IEC standards have been approved unanimously in September and October 2007 and were published as IS (International Standards) later that year. In IEC 61800-7, EtherCAT is a standardized communication technology for the SERCOS and CANopen drive profiles (also known as CiA 402). EtherCAT is also part of ISO 15745-4,[16] the standard for XML device description. Furthermore, SEMI has added EtherCAT to its standards portfolio (E54.20)[17] and approved the technology for usage in semiconductor and flat panel display manufacturing equipment. In April 2010, Edition 2 of IEC 61784-3[18] was accepted, which contains the Safety over EtherCAT Protocol. In September 2008, the EtherCAT Installation Profile was submitted to IEC 61784-5.[19]
Potra, S.; Sebestyen, G. (2006), "EtherCAT Protocol Implementation Issues on an Embedded Linux Platform", IEEE-TTTC International Conference on Automation, Quality and Testing, Robotics AQTR 2006, Cluj-Napora, Romania: IEEE, pp.420–425
Robertz, S. G.; Nilsson, K.; Henriksson, R.; Blomdell, A. (2007), "Industrial robot motion control with real-time Java and EtherCAT", 12th IEEE International Conference on Emerging Technologies and Factory Automation, Patras, Greece: IEEE
Cena, Gianluca; Cibrario Bertolotti, Ivan; Scanzio, Stefano; Valenzano, Adriano; Zunino, Claudio (2010), "On the accuracy of the distributed clock mechanism in EtherCAT", Factory Communication Systems (WFCS), 2010 8th IEEE International Workshop on, Nancy, France: IEEE, pp.43–52, doi:10.1109/WFCS.2010.5548638, S2CID14517885
↑ IEC 61158-2 (Ed.4.0), Industrial communication networks - Fieldbus specifications - Part 2: Physical layer specification and service definition
↑ IEC 61158-3/4/5/6-12 (Ed.1.0), Industrial communication networks - Fieldbus specifications - Part 3-12: Data-link layer service definition - Part 4-12: Data-link layer protocol specification - Part 5-12: Application layer service definition - Part 6-12: Application layer protocol specification -Type 12 elements (EtherCAT)
↑ IEC 61784-2 (Ed.1.0), Industrial communication networks - Profiles - Part 2: Additional fieldbus profiles for real-time networks based on ISO/IEC 8802-3
↑ IEC 61800-7-301/304 (Ed.1.0), Adjustable speed electrical power drive systems - Part 7-301: Generic interface and use of profiles for power drive systems - Mapping of profile type 1 to network technologies - Part 7-304: Generic interface and use of profiles for power drive systems - Mapping of profile type 4 to network technologies
↑ ISO 15745-4:2003/Amd 2:2007, Industrial automation systems and integration -- Open systems application integration framework - Part 4: Reference description for Ethernet-based control systems
↑ SEMI E54.20-1108 - Standard for Sensor/Actuator Network Communications for EtherCAT
↑ IEC 61784-3 Industrial communication networks - Profiles - Part 3: Functional safety fieldbuses
↑ IEC 61784-5 Industrial communication networks - Profiles - Part 5: Installation of fieldbuses
A distributed control system (DCS) is a computerized control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory control. This is in contrast to systems that use centralized controllers; either discrete controllers located at a central control room or within a central computer. The DCS concept increases reliability and reduces installation costs by localizing control functions near the process plant, with remote monitoring and supervision.
Profibus is a standard for fieldbus communication in automation technology and was first promoted in 1989 by BMBF and then used by Siemens. It should not be confused with the Profinet standard for Industrial Ethernet. Profibus is openly published as type 3 of IEC 61158/61784-1.
A fieldbus is a member of a family of industrial digital communication networks used for real-time distributed control. Fieldbus profiles are standardized by the International Electrotechnical Commission (IEC) as IEC 61784/61158.
Industrial Ethernet (IE) is the use of Ethernet in an industrial environment with protocols that provide determinism and real-time control. Protocols for industrial Ethernet include EtherCAT, EtherNet/IP, PROFINET, POWERLINK, SERCOS III, CC-Link IE, and Modbus TCP. Many industrial Ethernet protocols use a modified media access control (MAC) layer to provide low latency and determinism. Some microprocessors provide industrial Ethernet support.
The Precision Time Protocol (PTP) is a protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems. PTP is employed to synchronize financial transactions, mobile phone tower transmissions, sub-sea acoustic arrays, and networks that require precise timing but lack access to satellite navigation signals.
Fieldbus Foundation was an organization dedicated to a single international, interoperable fieldbus standard. It was established in September 1994 by a merger of WorldFIP North America and the Interoperable Systems Project (ISP). Fieldbus Foundation was a not-for-profit trade consortium that consisted of more than 350 of the world's suppliers and end users of process control and manufacturing automation products. Working together those companies made contributions to the IEC/ISA/FDI and other fieldbus standards development.
Foundation Fieldbus is an all-digital, serial, two-way communications system that serves as the base-level network in a plant or factory automation environment. It is an open architecture, developed and administered by FieldComm Group.
Actuator Sensor Interface is an industrial networking solution used in PLC, DCS and PC-based automation systems. It is designed for connecting simple field I/O devices in discrete manufacturing and process applications using a single two-conductor cable.
Profinet is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling equipment in industrial systems, with a particular strength in delivering data under tight time constraints. The standard is maintained and supported by Profibus and Profinet International, an umbrella organization headquartered in Karlsruhe, Germany.
In the field of Industrial Control Systems, the interfacing of various control components must provide means to coordinate the signals and commands sent between control modules. While tight coordination is desirable for discrete inputs and outputs, it is especially important in motion controls, where directing the movement of individual axes of motion must be precisely coordinated so that the motion of the entire system follows a desired path. Types of equipment requiring such coordination include metal cutting machine tools, metal forming equipment, assembly machinery, packaging machinery, robotics, printing machinery and material handling equipment. The Sercos interface is a globally standardized open digital interface for the communication between industrial controls, motion devices (drives) and input output devices (I/O). Sercos I and II are standardized in IEC 61491 and EN 61491. Sercos III is specified in standards IEC 61800-7; IEC 61784-1, -2, -3 and IEC 61158. Sercos is designed to provide hard real-time, high performance communications between industrial motion controls and digital servo drives.
Foundation Fieldbus H1 is one of the FOUNDATION fieldbus protocol versions. Foundation H1 (31.25 kbit/s) is a bi-directional communications protocol used for communications among field devices and to the control system. It utilizes either twisted pair, or fiber media to communicate between multiple nodes (devices) and the controller. The controller requires only one communication point to communicate with up to 32 nodes, this is a significant improvement over the standard 4–20 mA communication method which requires a separate connection point for each communication device on the controller system.
EtherNet/IP is an industrial network protocol that adapts the Common Industrial Protocol (CIP) to standard Ethernet. EtherNet/IP is one of the leading industrial protocols in the United States and is widely used in a range of industries including factory, hybrid and process. The EtherNet/IP and CIP technologies are managed by ODVA, Inc., a global trade and standards development organization founded in 1995 with over 300 corporate members.
Profisafe is a standard for a communication protocol for the transmission of safety-relevant data in automation applications with functional safety. This standard was developed jointly by several automation device manufacturers in order to be able to meet the requirements of the legislator and the IFA for safe systems. The required safe function of the protocol has been tested and confirmed by TÜV Süd. The PROFIBUS Nutzerorganisation e.V. in Karlsruhe supervises the standardization for the partner companies and organizes the promotion of this common interface.
Sercos III is the third generation of the Sercos interface, a standardized open digital interface for the communication between industrial controls, motion devices, input/output devices (I/O), and Ethernet nodes, such as PCs. Sercos III applies the hard real-time features of the Sercos interface to Ethernet. It is based upon and conforms to the Ethernet standard. Work began on Sercos III in 2003, with vendors releasing first products supporting it in 2005.
Parallel Redundancy Protocol (PRP) is a network protocol standard for Ethernet that provides seamless failover against failure of any network component. This redundancy is invisible to the application.
openSAFETY is a communications protocol used to transmit information that is crucial for the safe operation of machinery in manufacturing lines, process plants, or similar industrial environments. Such information may be e.g. an alert signal triggered when someone or something has breached a light curtain on a factory floor. While traditional safety solutions rely on dedicated communication lines connecting machinery and control systems via special relays, openSAFETY does not need any extra cables reserved for safety-related information. It is a bus-based protocol that allows for passing on safety data over existing Industrial Ethernet connections between end devices and higher-level automation systems – connections principally established and used for regular monitoring and control purposes. Unlike other bus-based safety protocols that are suitable for use only with a single or a few specific Industrial Ethernet implementations and are incompatible with other systems, openSAFETY works with a wide range of different Industrial Ethernet variants.
RAPIEnet was Korea's first Ethernet international standard for real-time data transmission. It is an Ethernet-based industrial networking protocol, developed in-house by LSIS offers real-time transmission and is registered as an international standard.
IEC/IEEE 61850-9-3 or PUP is an international standard for precise time distribution and clock synchronization in electrical grids with an accuracy of 1 μs. It supports precise time stamping of voltage and current measurement for differential protection, wide area monitoring and protection, busbar protection and event recording. It can be used to ensure deterministic operation of critical functions in the automation system. It belongs to the IEC 61850 standard suite for communication networks and systems for power utility automation.
Industrial automation systems consisting of several distributed controllers need a precise synchronization for commands, events and process data. For instance, motors for newspaper printing are synchronized within some 5 microseconds to ensure that the color pixels in the different cylinders come within 0.1 mm at a paper speed of some 20 m/s. Similar requirements exist in high-power semiconductors and in drive-by-wire vehicles. This synchronisation is provided by the communication network, in most cases Industrial Ethernet. Many ad-hoc synchronization schemes exist, so IEEE published a standard Precision Time Protocol IEEE 1588 or "PTP", which allows sub-microsecond synchronization of clocks. PTP is formulated generally, so concrete applications need a stricter profile. In particular, PTP does not specify how the clocks should operate when the network is duplicated for better resilience to failures.
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