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To EtherCAT® and beyond

ethercat
Figure 1 - Typical EtherCAT system showing the functions Microchip products can perform

In the last two decades there has been a great change in the way industrial systems communicate. Companies have moved from fieldbus-based systems to Ethernet-based communication systems. The strong growth of Ethernet-based industrial communications is expected to continue apace as the latest study by analyst MarketsandMarkets has found that the global Industrial Ethernet market is forecast to rise from $9.200 billion in 2020 to $13.700 billion. dollars in 2026, a CAGR of 7,3% during the research period.

It is no surprise that Industrial Ethernet has achieved such market share in such a relatively short period of time. Although improvements have been made to fieldbus-based systems, they still have some limitations. They are ideal for simple control functionality, but with more manufacturers working on implementing an Industry 4.0 strategy, these limitations become difficult to overcome. The most obvious limitation is speed, especially when it comes to applications that need very complex and precise control, such as robotics.

An Ethernet-based implementation is an obvious alternative. Ethernet has enough bandwidth to handle the vast majority of industrial use cases, even for the most demanding Industry 4.0 applications. It is a well-understood, cost-effective standard used throughout the world. It is flexible and can be used for many different applications, especially since older fieldbus branches can be easily and cheaply incorporated into the Ethernet backbone. For implementation and maintenance, there is no shortage of engineers who have worked with and understand Ethernet technology. Industry 4.0 requires a strong link between industrial operations and IT, so it makes sense to have communications systems that are based on the same standard. However, the Ethernet found in IT systems is not deterministic, and that is one of the most important requirements for control systems.

This lack has led various manufacturers and organizations to develop an Ethernet-based standard that is suitable for industrial use. The most popular of these new standards are Ethernet TSN, EtherNet/IP, PROFINET, and EtherCAT. Since their initial development, each of these protocols and other smaller or proprietary systems have found their own geographic or technical niche.

All protocols have their own advantages and disadvantages. In general, they take the concept of Ethernet as found in computing and adapt it to offer real-time operation. One of the Industrial Ethernet implementations does things a little differently: EtherCAT (Ethernet for Control Automation Technology) keeps the standard Ethernet physical layer and builds an entirely new deterministic protocol on top of it. The protocol uses a host controller, which is the only device that can create the EtherCAT frame. The frame is always the same length, and each device node on the network has an addressable area of ​​the frame dedicated to it. As the frame travels through the network, each node collects the control data and leaves the response information in its allocated space as it passes, without delaying the frame more than the hardware propagation delay and offering a speed of maximum effective data close to the line speed of 100Mbit/sg.

In other Industrial Ethernet implementations, performing the frame check, performing a CRC check, and going through the stack can take hundreds of microseconds. EtherCAT is designed to complete the entire process in just 125µs. That increased speed makes the system more responsive, which in turn makes the entire control application more efficient and safer. The EtherCAT device node is also much simpler than other Industrial Ethernet implementations, requiring only a single stack code (SSC) running on a modest microcontroller, which also reduces system complexity and cost.

However, the EtherCAT implementation is not the easiest to achieve. The most difficult barrier for designers is meeting cycle time requirements. Many manufacturers, especially those using motors, want to implement control algorithms at 8000 cycles per second, which is a cycle time of 125 µs. Although EtherCAT systems should easily achieve this figure, achieving it in practice has proven difficult and often requires extensive software writing and optimization. In addition, it can be expensive: a DIN rail EtherCAT controller to be placed next to a motor controller can cost hundreds of euros. However, you can get a custom design for almost ten times less.

evaluation board
Figure 2 – The LAN9255 evaluation board (EVB-LAN9255) allows engineers to develop using an embedded Cortex M4F microcontroller with an EtherCAT device driver

a new solution

Microchip has been in the EtherCAT market since 2012. The company introduced its first EtherCAT device controller (ESC), the LAN9252, in 2015. That market entry proved to be a success, and it also allowed the company to gather information about where were the points of tension in the market. He found that users wanted an easier way to meet cycle time requirements and a number of features that would allow them to add value to their implementations and give them better insight into how EtherCAT works.

The feedback received led Microchip to develop its second generation of ESC solutions, which were released in September 2020. The LAN9253 and LAN9254 devices are 3-port ESCs that feature integrated dual Ethernet PHYs with a full-duplex 100BASE-TX transceiver and operation at 100Mbps.

The most important improvement the company made to the new ESCs was to adapt the design so that designers could meet cycle time targets with very little software optimization. The new devices have also simplified the implementation of EtherCAT nodes by reducing design time and the necessary bill of materials. Typical EtherCAT implementations use an ESC, a microcontroller, and an EEPROM, and the EEPROM houses the configuration for the ESC. Microchip has developed a technique that effectively emulates EEPROM. The ESC uses a function call to get instructions directly from the host microcontroller without affecting performance, making the physical EEPROM unnecessary.

The new ICs have also been designed with a feature that reduces the number of crystals required for synchronization. Many industrial designs use multi-axis controllers for applications like robotics. These designs can require up to six different control circuits to operate a multi-axis robotic arm. Before, each of those circuits needed its own crystal for synchronization. The new ICs include a method to accurately replicate the timing and jitter system for all six circuits using a single crystal, eliminating the need for five additional crystals and further reducing system cost.

Both devices also offer other features that make EtherCAT systems easier to deploy and operate. The EtherCAT protocol was designed without physical layer diagnostics, so users only learned of failures, such as cable degradation, when they started experiencing CRC errors and other issues. Microchip designed the ability to monitor cable status at any time, allowing users to see failures before they become a problem, a key Industry 4.0 principle.

The LAN9253 is housed in a QFN package, closely replicating the pinout of the LAN9252 package so that customers can take advantage of design enhancements with minimal redesign. The LAN9254 has an additional 16 I/O pins that allow the ESC to function as a simple controller without the need for a microcontroller. Since the area of ​​the frame used by the device node and the propagation delay are known, the ESC bits can be assigned to offsets in the frame and the 32 I/O lines to allow field equipment to connect directly to the EtherCAT network.

Many customers asked us to include a controller to offer an all-in-one ESC solution. This year, Microchip has released the LAN9255 which adds a Cortex-M4F microcontroller. The MCU is fast enough to handle the EtherCAT requirements, while also acting as an application processor for the control system. The processor's floating-point unit helps with more complex algorithms, such as those needed for motor control. Ethernet sockets with code support for version 3 of SNMP have also been added to give designers more flexibility in linking operational technology to IT systems.

Conclusion

Microchip's LAN9253 and LAN9254 ICs have made EtherCAT nodes easier to deploy and maintain, reducing time and cost by eliminating the need for some supporting components, facilitating the software optimization process, and adding the ability to analyze the net. The new LAN9255 CI takes this trend one step further by eliminating the need for an external host controller and providing developers with an EtherCAT node and field control solution in a single package. Use of the Microchip MPLAB X Harmony framework further accelerates time to market by allowing software for communication and control to be written and optimized in an easy-to-use, single-user environment.

All of the devices described in this article are now available, shipped in production volumes, and supported by Microchip's design verification services.

By Ian Saturley, Director of Strategic Marketing, USB and Networking Group – Microchip Technology