What are the characteristics of EtherCAT network communication?

In normal applications, KUKA, riveting equipment, laser welding and other equipment use EtherCAT communication extensively. Let's introduce it below.

1. EtherCAT protocol processing is completely performed in

The protocol is flexibly configurable. The process can be expanded from 1 to 64 kbit.

So it is possible to directly access the module:

The Ethernet protocol in accordance with the IEEE 802.3 standard allows access to individual devices without any additional bus. The physical layer in the device is converted from 100BASE-TX or –FX to E-bus to meet the needs of modular devices such as terminal blocks. The E-bus type (LVDS) within the terminal block is not exclusive and can also be used for 10 Gbit Ethernet. At the end of the terminal block, the physical bus characteristics are converted back to the 100BASE-TX standard.

The Ethernet MAC integrated on the motherboard is sufficient for use as hardware in the master device. (Direct Memory Access) is used to transfer data to the main memory, relieving the burden of accessing data. The same principle is used in the multi-card from Beckhoff, which bundles up to 4 Ethernet channels in one PCI slot.

2. EtherCAT Performance

EtherCAT takes networking performance to a new level.

The update time for 1000 I/Os is just 30 µs, including the I/O cycle time. Up to 1486 bytes of process data can be exchanged in a single Ethernet frame, which corresponds to almost 12000 digital inputs and outputs, and this data is transmitted in just 300 µs.

The communication with 100 servo axes is performed every 100 µs. The actual position and status of all axes with command values ​​and control data can be updated within this cycle time. The distributed technology enables the synchronization deviation of the axes to be less than 1 microsecond.

The ultra-high-performance EtherCAT technology can realize control concepts that traditional fieldbus systems cannot achieve.

In this way, ultra-high-speed control loops can also be formed through the bus. Functions that previously required local dedicated hardware support can now be mapped in software. Huge bandwidth resources enable status data to be transmitted in parallel with any data. EtherCAT adapts communication technology to the super computing power of modern PCs. The bus system is no longer a bottleneck for control concepts, and distributed I/O may run faster than most local I/O interfaces.

This network performance advantage is particularly evident in small controllers with relatively moderate computing power. The EtherCAT cycle time is so short that it can be completed between two control cycles. As a result, the controller always has access to input data; the outputs are addressed with minimal delay. Without increasing the computing power itself, the response behavior of the controller can be significantly improved.

Thanks to slave hardware integration and direct memory access to the network controller master, the entire protocol processing is implemented in hardware and is therefore completely independent of the real-time operating system, CPU performance or software implementation of the protocol stack.

The update time for 1000 I/Os is just 30 µs, which also includes the I/O cycle time.

A single Ethernet frame can exchange up to 1486 bytes of process data, which corresponds to almost 12,000 digital inputs and outputs, and transmit this data in just 300 µs.

The communication of 100 servo axes is also very fast: the actual position and status of all axes with command values ​​and control data can be updated every 100µs, and the distributed clock technology makes the axis synchronization deviation less than 1 microsecond. Even with this performance, the bandwidth is still sufficient to realize asynchronous communication, such as TCP/IP, parameters or uploading diagnostic data.

The ultra-high-performance EtherCAT technology can realize control concepts that traditional fieldbus systems cannot reach. EtherCAT adapts communication technology to the super computing power of modern industrial PCs. The bus system is no longer a bottleneck for control concepts, and distributed I/O may run faster than most local I/O interfaces. The principle of EtherCAT technology is malleable and is not bound by a communication rate of 100 M bps. It may even be expanded to 1000 M bps Ethernet.

3. EtherCAT topology

Line, tree or star: EtherCAT supports almost any type of topology.

Therefore, the bus structure or line structure named after the field bus can also be used for Ethernet and is not limited by the number of cascades or hubs.

The most efficient system wiring method is to combine line, branch or tree topologies. Because the required interfaces are already available in many devices such as I/O modules, no additional switches are required.

Of course, the traditional Ethernet-based star topology can still be used.

Different cables are available for increased wiring flexibility: Flexible, economical standard Category 5e Ethernet cables can transmit signals in 100BASE-TX mode with a maximum cable length of 100 m between two devices.

A complete combination of different Ethernet connections (such as different fiber optic and copper cables) can also be implemented via switches or media.

The signal variant can be selected individually for each cable span. Since up to 65535 devices can be connected, the capacity of the network is virtually unlimited.

EtherCAT uses full-duplex Ethernet physical layer, and the slave station may have two or more ports. If the device does not detect other devices downstream, the slave station controller will automatically close the corresponding port and return the Ethernet frame. Due to the above characteristics, EtherCAT supports almost all network topologies, including bus, tree or star. The bus topology commonly used in fieldbus can also be used in Ethernet.

The topology of EtherCAT can be any combination of network cables, branches or stubs. Devices with three or more Ethernet interfaces can be used as taps, and network switches are not necessarily required. Due to the use of the 100BASE-TX Ethernet physical layer, the distance between two devices can be up to 100 meters, and a network in an EtherCAT segment can have up to 65535 devices. If the EtherCAT network uses a ring topology (the master device needs to have two communication ports), the network also has cable redundancy.

4. EtherCAT supports hot connection

Many applications require changing the I/O configuration during operation. For example, machining centers with changing requirements, tool systems or optimized transmission systems, flexible workpiece actuators, or printing presses that can shut down printing units individually. These requirements have been taken into account in the protocol structure of the EtherCAT system: the hot connection function can connect or disconnect various parts of the network, or reconfigure "on the fly", providing flexible response capabilities for changing configurations.

5. Safety over EtherCAT

EtherCAT has an enhanced protocol version called Safety over EtherCAT, which can perform safety-related communication and general control communication on the same network. This safety communication is based on the application layer of EtherCAT and does not affect the underlying communication protocol. Safety over EtherCAT has passed IEC 61508 and meets the requirements of Safety Integrity Level (SIL) 3.

To achieve EtherCAT safety data communication, we have opened the Safetyover EtherCAT protocol, which has been made public within the ETG organization. The protocol has been identified by the German Technical Inspectorate (TÜV) as meeting the SIL3 level requirements defined in IEC61508. The implementation of the EtherCAT safety protocol on the device must meet the requirements of the safety goals. The corresponding related requirements must also be taken into account.

EtherCAT is used as a single channel for the transmission of safety and non-safety data. The transmission medium is considered a "black channel" and is not included in the safety protocol.

The safety data message in the EtherCAT process data includes the safety process data and the required data backup. This "container" is safely parsed at the application layer of the device. Communication remains single-channel. This complies with model A in the annex to IEC61784-3. Therefore, the safety protocol can also be transmitted via other communication systems, backplanes or WLAN. The transmission cycle can be shortened as required without affecting the residual error rate. Safety over EtherCAT The cyclic exchange of safety data between the master and slaves is called a monitored connection. A master can establish and monitor connections to several different slaves.

Safety elements can be used wherever they are needed in the automation system. Local input and output elements of different sizes can be used in the system. Additional inputs and outputs can be expanded as required using safety or non-safety bus terminals. The safety logic is also embedded in the network. This allows control tasks to continue to be processed without the standard safety extension. The local safety logic required for the safety input and output functions is implemented by intelligent safety bus terminals. This saves costs associated with expensive safety PLCs and allows the logic functions to be tailored to the task at hand. Only the safety EtherCAT master and the assigned safety slaves are routed via the non-safety standard PLC.

§ This protocol has no restrictions on secure data length, communication medium or baud rate.

§ EtherCAT is used as a “black channel”, i.e. the communication system plays no role in the safety processing.

§ The protocol is certified to meet the SIL3 level defined by IEC61508

§ Products offering EtherCAT safety functionality have been available on the market since 2005.