EtherCAT
EtherCAT ( ether net for C ontrol A utomation T echnology ) is one of the company Beckhoff Automation initiated real-time Ethernet . The protocol disclosed in IEC standard 61158 is suitable for both hard and soft real-time requirements in automation technology . The technology is protected by patents and is licensed by Beckhoff. The licensing of master implementations is permanently free of charge, the specification must be fully complied with. License fees are charged for slave controllers.
The focus of the development of EtherCAT was on short cycle times (≤ 100 µs), low jitter for exact synchronization (≤ 1 µs) and low hardware costs.
EtherCAT properties
Working principle
EtherCAT differs significantly from many other Industrial Ethernet solutions. While with these the standard Ethernet frame sent by the master (according to IEEE 802.3) is first received in each connection, then interpreted and the process data copied, with EtherCAT and Sercos_III the slave devices extract the data intended for them, while the telegram the Device runs through. Input data are also inserted into the telegram in the process. A frame is not completely received before it is processed, but processing begins as early as possible. Sending is also carried out with a minimal offset of a few bit times.
ISO / OSI reference model
Additional information on the graphic:
- The TCP / IP stack shown here is not required for typical field devices.
- The EtherCAT masters can display all data of an EtherCAT slave with names and data types using standard mechanisms without complex tools.
- EtherCAT uses the Ethernet standard (IEEE 802.3 - Ethernet MAC and PHY) without modifications.
protocol
The EtherCAT protocol optimized for process data is sent within a standard Ethernet frame using its own EtherType (0x88A4). The EtherCAT telegram can consist of several sub-telegrams (EtherCAT commands), each of which serves a memory area of the logical process image, which is up to 4 gigabytes in size.
The data order is independent of the physical order of the participants in the network, it can be addressed as desired. Broadcast , multicast and cross communication between slaves are possible.
topology
The EtherCAT transmission method is based on the full duplex properties of Ethernet. At the cabling level, EtherCAT enables a wide variety of topologies such as line, tree, ring, star and their combinations. This is linked to various communication properties such as line redundancy, hot connect of segments, device replacement while the network is running or master redundancy with hot standby .
The combination of topology variants with different network architectures, such as subordinate or neighboring control systems with continuous synchronization, opens up many possibilities. So you don't need any additional switches .
The Fast Ethernet physics allows a line length of a maximum of 100 m between two participants, the E-Bus ( LVDS ) is only provided as a bit transmission layer ( physical layer ) for modular devices . The signal variant can be selected individually for each line section. Fiber-optic cables are used for larger distances or for complete galvanic separation between two slaves . With single mode fiber , up to 20 km can be bridged between two participants. Since up to 65535 participants can be connected to each network segment, the entire network expansion is almost unlimited.
Synchronization
The exact synchronization is always of particular importance when spatially distributed processes require simultaneous actions, e.g. B. where several servo axes are to execute coordinated movements at the same time.
The most powerful approach to synchronization is the exact synchronization of distributed clocks (DC). The time of the main clock is transferred to the slave clocks via EtherCAT and these are readjusted in a time-compensated manner. With EtherCAT, the main clock is in a slave device, so that no special hardware is required in the master for this either. The synchronization accuracy is well below 1 µs, with 300 participants and a cable length of 120 m, deviations of ± 20 ns were achieved.
Performance data
Due to the hardware integration in the slave and DMA access to the network card in the master, all protocol processing takes place in hardware and is therefore independent of the runtime of the protocol stack , CPU performance or software implementation.
| Process data | Update time |
|---|---|
| 256 distributed digital I / O | 10 µs |
| 1000 distributed digital I / O | 30 µs |
| 200 analog I / O | 50 µs at 20 kHz |
| 100 servo axes, 8 bytes each of input and output data | every 100 µs |
| 1 fieldbus master gateway (1486 bytes of input and 1480 bytes of output data) | 150 µs |
The utilization of bandwidth is maximized because a separate frame is not always required for each participant and each date. This results in extremely short cycle times of ≤ 100 µs. By using the full-duplex properties of 100BASE-TX , effective data rates of over 100 Mbit / s (> 90 percent user data rate of 2 × 100 Mbit / s) can be achieved.
The EtherCAT technology principle is scalable and not tied to 100 Mbit / s. Extensions to Gigabit Ethernet were presented with EtherCAT G and EtherCAT G10 at SPS IPC-Drives in November 2018.
diagnosis
The fast and precise detection of malfunctions is one of many diagnostic features that EtherCAT offers.
Bit errors in the transmission are reliably detected by evaluating the CRC checksum: the 32-bit CRC polynomial has a minimum Hamming distance of 4. In addition to the breakpoint detection and localization, the protocol, transmission physics and topology of the EtherCAT system allow individual quality monitoring of each individual transmission link. The automatic evaluation of the corresponding error counters enables the exact localization of critical network sections.
For more information, see the Monitoring section below.
EtherCAT connection development for CANopen and Sercos devices
The device profiles describe the application parameters and the functional behavior of the devices, including the device class-specific state machines. The following software interfaces are offered for existing device profiles. A manufacturer-side migration from the previous fieldbus to EtherCAT by adapting the firmware and hardware is thus made much easier.
CAN application protocol over EtherCAT (CoE)
CANopen device and application profiles are available for a wide variety of device classes and applications: Starting with the I / O modules via drives (e.g. drive profile CiA 402 standardized as IEC 61800-7-201 / 301), encoders ( CiA 406), proportional valves and hydraulic controllers (CiA 408), through to application profiles. EtherCAT will then replace CAN .
Servodrive profiles over EtherCAT (SoE)
SERCOS interface is a powerful real-time communication interface, especially for demanding motion control applications. The SERCOS profile for servo drives and communication technology are standardized in IEC 61800-7. This standard contains the mapping of the SERCOS servodrive profile to EtherCAT (IEC 61800-7-304).
Other protocols
Ethernet over EtherCAT (EoE)
Any Ethernet device can be connected within the EtherCAT segment via so-called switch ports. The Ethernet frames are tunneled through the EtherCAT protocol , as is usual with Internet protocols (e.g. TCP / IP , VPN , PPPoE ( DSL ) etc.). The EtherCAT network is fully transparent for the Ethernet devices and the EtherCAT real-time properties are not impaired.
File Access over EtherCAT (FoE)
This very simple protocol, based on TFTP , enables access to any data structure in the device. So z. For example, a uniform firmware upload to devices is possible - regardless of whether they support TCP / IP.
Safety over EtherCAT (FSoE)
Parallel to the EtherCAT development, a fieldbus-independent safety protocol was also developed, which is available for EtherCAT as "Safety over EtherCAT" (FSoE = Fail Safe over EtherCAT). Functional safety can thus be implemented with EtherCAT. The protocol and implementation are certified by TÜV and meet Safety Integrity Level 3 according to IEC 61508. Safety over EtherCAT has been internationally standardized in IEC 61784-3-12 since 2010.
Safety over EtherCAT does not cause any restrictions in terms of transmission speed and cycle time, since EtherCAT is used as a single-channel communication medium. The transport medium is viewed as a “black channel” and not included in the security assessment.
Monitoring
Since EtherCAT standard uses Ethernet frames in accordance with IEEE 802.3, any commercially available Ethernet monitoring tool is suitable for monitoring the EtherCAT communication. In addition, there is free parser software for Wireshark (formerly Ethereal, an open source monitoring tool) and the Microsoft network monitor , with which recorded EtherCAT data traffic can be processed and displayed.
integration
Existing networks such as CANopen , DeviceNet and Profibus can be seamlessly integrated into the EtherCAT environment via gateways and also offer a trip-free migration path from the classic fieldbus to EtherCAT. This protects existing investments.
Thanks to the high performance of EtherCAT, communication with outsourced fieldbus masters is just as fast as with classic cards connected via PCI or other backplane buses. Since decentralized fieldbus interfaces lead to shorter expansions of the fieldbuses, they can often be operated with even higher baud rates than would have been possible with the classic architecture.
implementation
master
Masters can be implemented as a software solution on any Ethernet MAC. There is code from different manufacturers and for different operating systems, including several open source projects (see links).
Due to the relocated mapping in the slave hardware, there are no great demands on the CPU performance of the master; the master already receives the data as a fully sorted process image.
Slave
In contrast to standard Ethernet, the EtherCAT frames are processed by the slaves on the fly. This means that hardware-integrated EtherCAT slave controllers (ESC) must be used on the slave side. ESC are designed as ASICs or implemented on an FPGA basis. The first standard microprocessors with an EtherCAT slave interface have also been on the market since the beginning of 2012.
No additional microcontroller is required for simple devices . In the case of more complex devices with microcontrollers, the communication performance with EtherCAT is almost independent of the performance of the controller used. The requirements for the microcontroller are therefore dictated by the local application, e.g. B. the drive control. Complex devices, especially when using CAN application protocol over EtherCAT (CoE) , require a protocol stack that implements the CoE protocol. In EtherCAT Product Guide diverse EtherCAT slave stacks are listed from various commercial sources. In addition, there is an open source stack called SOES and free code from Beckhoff, but not open source, for an EtherCAT slave stack. Development tools and frameworks are also available, which are based on the EtherCAT slave stack code.
Applications
Control and regulation
A high level of data integrity, data security and synchronicity are required to control and regulate physical processes. EtherCAT was specially designed for these applications and meets all requirements for fast control.
Measuring systems
Modern measuring systems are characterized by multi-channel functionality, synchronicity and accuracy. The protocol properties of EtherCAT guarantee efficient synchronous data throughput. The network properties given by Ethernet enable a measurement network with distributed measurement modules.
User organization: EtherCAT Technology Group
The EtherCAT Technology Group was founded in 2003 and, in terms of the number of its members, is today the largest user organization in terms of Industrial Ethernet worldwide.
It offers its members implementation support and training, organizes interoperability tests (so-called plug-fests) and promotes the development and dissemination of the technology with the help of members and offices in Germany, China, Japan, Korea and the USA.
The ETG brings together end users from different industries, machine manufacturers and providers of high-performance control technology to support and promote EtherCAT technology. The diversity of industries ensures that EtherCAT is optimally prepared for a wide range of applications. With their qualified feedback, the system partners ensure that the hardware and software modules can be easily integrated into all of the required device classes.
The Conformance Test Tool (CTT) developed with the help of ETG members ensures the interoperability and protocol conformity of the EtherCAT devices.
International standardization
EtherCAT has been an IEC standard since 2005 . The EtherCAT Technology Group is the official standardization partner of the IEC working groups for digital communication.
The integration into the international standards IEC 61158 (protocols and services) and IEC 61784-2 (communication profiles for the specific device classes) has taken place. In IEC 61800-7 (drive profiles and communication), EtherCAT is standardized as a communication technology for the SERCOS and the CANopen drive profile. EtherCAT is also included in ISO 15745-4 (device description with XML ).
EtherCAT has also been a SEMI standard since September 2007: the E54.20 describes the use of the technology in semiconductor and flat-panel display production systems.
See also
literature
- IEC 61158-3 / 4/5 / 6-12: 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 specification, Part 6-12: Application layer protocol specification
- IEC 61784-2: Industrial communication networks - Profiles, Part 2: Additional fieldbus profiles for real-time networks based on ISO / IEC 8802-3
- IEC 61784-3: Industrial communication networks - Profiles, Part 3: Functional safety fieldbuses
- IEC 61784-5: Industrial communication networks - Profiles, Part 5: Installation of fieldbuses
- IEC 61800-7: Adjustable speed electrical power drive systems
- ISO 15745-4: Industrial automation systems and integration
- Klaus Kafka: A field report on the various real-time Ethernet systems . In: Günther Brandenburg (Ed.): SPS IPC DRIVES 2006: Trade Fair & Congress 28. – 30. Nov. 2006, Nuremberg . VDE-Verlag, Berlin / Offenbach 2006, ISBN 978-3-8007-2994-4
- Frithjof Klasen, Volker Oestreich, Michael Volz: Industrial communication with fieldbus and Ethernet . VDE-Verlag, Berlin / Offenbach 2010, ISBN 978-3-8007-3297-5
Web links
- EtherCAT Technology Group
- Open source EtherCAT master / slave library for Linux, PREEMPT_RT or Xenomai
- Open Source EtherCAT Master for Linux / Real Time Kernel
- Semiconductor Equipment and Materials International
Individual evidence
- ↑ https://www.ethercat.org/de/faq.html#788
- ↑ EtherCAT - the Ethernet Fieldbus , section CAN application layer over EtherCAT (CoE) (English / Japanese / Chinese)
- ↑ Wireshark
- ↑ White Paper: EtherCAT on Sitara AM335x ARM Cortex-A8 Microprocessors ( Memento of the original from November 7, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; English; 620 kB)
- ↑ http://openethercatsociety.github.io/doc/soes/index.html
- ↑ http://www.beckhoff.de/default.asp?ethercat/et9300.htm
- ↑ http://www.embedded-communication.com/ethercat/ethercat-slave-entwicklung/
