Abstract: Industrial Ethernet technology is a research hotspot in industrial control industry. EtherCAT technology is gaining attention of more and more R&D personnel because of its high speed, simplicity and ease of implementation. This article introduced the principle and protocol form of EtherCAT technology in detail, and combined with TMS320LF2407 to give a concrete implementation of EtherCAT slave.
I. INTRODUCTION Fieldbus has been the mainstream solution for field-level communication systems in the field of factory automation and process automation for the past ten years. However, with the continuous progress and development of automation control systems, traditional fieldbus technology has been difficult to meet the growing needs of users in many applications. Ethernet has achieved great success on local area networks and the Internet. In the entire enterprise information system, Ethernet has been used successfully in market management, production management, and process monitoring. If Ethernet can be introduced on the underlying device network, not only can the field device layer, process control layer, and management layer be easily integrated at the vertical level, but also the integration costs of devices from different manufacturers at the horizontal level can be reduced.
At present, industrial Ethernet technology has become a research hotspot in the field of industrial control. Many automation companies have launched their own industrial Ethernet solutions. At present, the main industrial Ethernet standards are the following: Modbus/TCP, EtherNet/IP, Profinet, Powerlink, EtherCAT, and EPA developed in China. Compared with traditional control networks, Industrial Ethernet has many advantages such as wide application, support for all programming languages, rich hardware and software resources, easy connection to the Internet, and seamless connection between office automation networks and industrial control networks.
EtherCAT (Ethernet for Control Automation Technology) is an industrial Ethernet technology developed by German automation company Beckhoff. The technology is gaining attention of more and more product developers because of its high speed, simplicity and ease of implementation. At the end of 2003, the ETG (Ethernet Technology Group) organization was established to take charge of the promotion and promotion of EtherCAT technology. Currently, the organization currently has more than 700 members, and many member organizations have developed products based on EtherCAT.
Second, EtherCAT technological principle EtherCAT is a real-time Ethernet field bus system, this agreement can be used for the optimal transmission of the process data. The EtherCAT protocol can include several EtherCAT messages, each serving a specific memory area of ​​a logical process image area, which can be up to 4 GB bytes. The order of the data to be transmitted and received does not depend on the physical order of the Ethernet terminals in the network, and can be freely addressed.
As a real-time Ethernet protocol, the OSI model of an EtherCAT slave can be briefly described in Figure 1. In Figure 1, the OSI model of the open system interconnection defined by the ISO International Standards Organization is compressed into a three-layer model with a physical layer, a data link layer, and an application layer. The physical layer provides a physical link for the transmission of network signals. The main task of the data link layer is to extract data from Ethernet frames within a specific “time window†and insert the data to be output into Ethernet frames, and check and verify the data. If the action cannot be completed within a specific time window, the action is considered to have failed. The role of the application layer is to process data link layer requests and respond appropriately.
The EtherCAT protocol itself determines that it does not need to receive Ethernet packets, decode it, and then copy the process data to each device. It has a master-slave data exchange principle and requires the master station and slave station to work together. Therefore, EtherCAT is ideal for communication between master and slave controllers. The Ethernet frame transmitted by the EtherCAT master station contains all I/O slave data. Messages are transferred between I/O slaves. Each slave acquires data in a very short time and writes the data to be sent to the Ethernet. The corresponding position of the network frame and then passes the message to the next slave station. After the last slave is processed, the message is passed back to the EtherCAT master.
figure 2
The EtherCAT protocol structure is shown in Figure 2. Figure 2 shows that EtherCAT fully utilizes the bandwidth of the IO layer because Ethernet frames transmitted and received compress a large amount of device data. EtherCAT protocol is used for data transmission. The available data transmission rate can reach over 90%, 100 Mbit/s. Full duplex features are fully utilized. According to statistics, it takes only 30 microseconds to process 1,000 digital I/Os and only 50 microseconds to process 200 16-bit analog signals, that is, the sampling frequency reaches 20 kHz. This real-time Ethernet protocol is well-suited for applications that require rapid control, and can truly use Ethernet at the sensor/actuator level. The EtherCAT protocol itself determines that it supports almost any topology type, including line, tree, star, etc., and is not limited to the number of cascaded switches or hubs.
In the aspect of fault diagnosis, EtherCAT can effectively detect bit failures during data transmission through CRC check, and EtherCAT can perform breakage detection and fault location through matching check. In addition, the protocol of the EtherCAT system can also perform quality monitoring for each transmission segment separately. The automatic assessment associated with the error counter can also accurately locate critical network segments.
III. Implementation of EtherCAT The realization of EtherCAT technology includes master station realization and slave station realization. The EtherCat master station does not require a dedicated communication processor. Instead, it only needs to use a passive NIC card or an integrated Ethernet MAC device on the motherboard. The protocol can be identified and encapsulated in the host CPU using software. EtherCat can implement up to 1486 bytes of distributed process data communication in a single Ethernet frame. In order to facilitate the development of the main station, the EtherCat organization now provides sample code for the main station, which can be easily embedded into a real-time operating system to accelerate the project development process. The human-machine interface of the EtherCAT master used in this paper is shown in Figure 3.
EtherCat slaves are implemented using dedicated hardware. Currently, several manufacturers provide EtherCAT slave controllers, and they can also purchase licensed binary codes at one time, implementing slave controller functions through inexpensive FPGAs. The dedicated hardware implementing the slave station has two MAC addresses, which can be easily extended to two network ports. The purpose is to facilitate cascading and form various topologies.
In this paper, TI's 16-bit processor TMS320LF2407 is used as a microprocessor and Beckhoff's ET1100 is used as an industrial Ethernet Ethercat protocol communication controller. The TMS320LF2407 implements the application layer of the EtherCat protocol. It can access the DPRAM internal to the ET1100 through a 16-bit parallel port. The ET1100 has two MII interfaces that implement the data link layer of the EtherCat protocol in hardware. The two physical layer chips that are externally extended implement the physical layer of Industrial Ethernet. The role of the network transformer is to achieve isolation and impedance matching. The data communication speed between the master station PC and the slave station reaches 100 Mbit/s. The specific block diagram of the implementation of the slave station is shown in Figure 4.
IV. CONCLUSIONS AND PROSPECTS As an industrial automation Ethernet solution, EtherCAT is gaining popularity among more and more R&D personnel because of its high speed, simplicity and ease of implementation. There have been several manufacturers in the world developing their own master station products and from Station chips, there are also many domestic manufacturers have begun to focus on product development of the technology. The Xinhua Group R&D Center has already taken the lead in domestically implementing the EtherCAT technology productization, successfully developed the first domestic DCSTisNet-E1000 based on EtherCAT, and led the development of automated products based on EtherCAT technology in China.
I. INTRODUCTION Fieldbus has been the mainstream solution for field-level communication systems in the field of factory automation and process automation for the past ten years. However, with the continuous progress and development of automation control systems, traditional fieldbus technology has been difficult to meet the growing needs of users in many applications. Ethernet has achieved great success on local area networks and the Internet. In the entire enterprise information system, Ethernet has been used successfully in market management, production management, and process monitoring. If Ethernet can be introduced on the underlying device network, not only can the field device layer, process control layer, and management layer be easily integrated at the vertical level, but also the integration costs of devices from different manufacturers at the horizontal level can be reduced.
At present, industrial Ethernet technology has become a research hotspot in the field of industrial control. Many automation companies have launched their own industrial Ethernet solutions. At present, the main industrial Ethernet standards are the following: Modbus/TCP, EtherNet/IP, Profinet, Powerlink, EtherCAT, and EPA developed in China. Compared with traditional control networks, Industrial Ethernet has many advantages such as wide application, support for all programming languages, rich hardware and software resources, easy connection to the Internet, and seamless connection between office automation networks and industrial control networks.
EtherCAT (Ethernet for Control Automation Technology) is an industrial Ethernet technology developed by German automation company Beckhoff. The technology is gaining attention of more and more product developers because of its high speed, simplicity and ease of implementation. At the end of 2003, the ETG (Ethernet Technology Group) organization was established to take charge of the promotion and promotion of EtherCAT technology. Currently, the organization currently has more than 700 members, and many member organizations have developed products based on EtherCAT.
Second, EtherCAT technological principle EtherCAT is a real-time Ethernet field bus system, this agreement can be used for the optimal transmission of the process data. The EtherCAT protocol can include several EtherCAT messages, each serving a specific memory area of ​​a logical process image area, which can be up to 4 GB bytes. The order of the data to be transmitted and received does not depend on the physical order of the Ethernet terminals in the network, and can be freely addressed.
As a real-time Ethernet protocol, the OSI model of an EtherCAT slave can be briefly described in Figure 1. In Figure 1, the OSI model of the open system interconnection defined by the ISO International Standards Organization is compressed into a three-layer model with a physical layer, a data link layer, and an application layer. The physical layer provides a physical link for the transmission of network signals. The main task of the data link layer is to extract data from Ethernet frames within a specific “time window†and insert the data to be output into Ethernet frames, and check and verify the data. If the action cannot be completed within a specific time window, the action is considered to have failed. The role of the application layer is to process data link layer requests and respond appropriately.
Figure 1 The OSI model of EtherCAT
The EtherCAT protocol itself determines that it does not need to receive Ethernet packets, decode it, and then copy the process data to each device. It has a master-slave data exchange principle and requires the master station and slave station to work together. Therefore, EtherCAT is ideal for communication between master and slave controllers. The Ethernet frame transmitted by the EtherCAT master station contains all I/O slave data. Messages are transferred between I/O slaves. Each slave acquires data in a very short time and writes the data to be sent to the Ethernet. The corresponding position of the network frame and then passes the message to the next slave station. After the last slave is processed, the message is passed back to the EtherCAT master.
figure 2
The EtherCAT protocol structure is shown in Figure 2. Figure 2 shows that EtherCAT fully utilizes the bandwidth of the IO layer because Ethernet frames transmitted and received compress a large amount of device data. EtherCAT protocol is used for data transmission. The available data transmission rate can reach over 90%, 100 Mbit/s. Full duplex features are fully utilized. According to statistics, it takes only 30 microseconds to process 1,000 digital I/Os and only 50 microseconds to process 200 16-bit analog signals, that is, the sampling frequency reaches 20 kHz. This real-time Ethernet protocol is well-suited for applications that require rapid control, and can truly use Ethernet at the sensor/actuator level. The EtherCAT protocol itself determines that it supports almost any topology type, including line, tree, star, etc., and is not limited to the number of cascaded switches or hubs.
In the aspect of fault diagnosis, EtherCAT can effectively detect bit failures during data transmission through CRC check, and EtherCAT can perform breakage detection and fault location through matching check. In addition, the protocol of the EtherCAT system can also perform quality monitoring for each transmission segment separately. The automatic assessment associated with the error counter can also accurately locate critical network segments.
III. Implementation of EtherCAT The realization of EtherCAT technology includes master station realization and slave station realization. The EtherCat master station does not require a dedicated communication processor. Instead, it only needs to use a passive NIC card or an integrated Ethernet MAC device on the motherboard. The protocol can be identified and encapsulated in the host CPU using software. EtherCat can implement up to 1486 bytes of distributed process data communication in a single Ethernet frame. In order to facilitate the development of the main station, the EtherCat organization now provides sample code for the main station, which can be easily embedded into a real-time operating system to accelerate the project development process. The human-machine interface of the EtherCAT master used in this paper is shown in Figure 3.
Figure 3 Test EtherCAT master man-machine interface
EtherCat slaves are implemented using dedicated hardware. Currently, several manufacturers provide EtherCAT slave controllers, and they can also purchase licensed binary codes at one time, implementing slave controller functions through inexpensive FPGAs. The dedicated hardware implementing the slave station has two MAC addresses, which can be easily extended to two network ports. The purpose is to facilitate cascading and form various topologies.
In this paper, TI's 16-bit processor TMS320LF2407 is used as a microprocessor and Beckhoff's ET1100 is used as an industrial Ethernet Ethercat protocol communication controller. The TMS320LF2407 implements the application layer of the EtherCat protocol. It can access the DPRAM internal to the ET1100 through a 16-bit parallel port. The ET1100 has two MII interfaces that implement the data link layer of the EtherCat protocol in hardware. The two physical layer chips that are externally extended implement the physical layer of Industrial Ethernet. The role of the network transformer is to achieve isolation and impedance matching. The data communication speed between the master station PC and the slave station reaches 100 Mbit/s. The specific block diagram of the implementation of the slave station is shown in Figure 4.
Figure 4 Schematic diagram of the slave station
IV. CONCLUSIONS AND PROSPECTS As an industrial automation Ethernet solution, EtherCAT is gaining popularity among more and more R&D personnel because of its high speed, simplicity and ease of implementation. There have been several manufacturers in the world developing their own master station products and from Station chips, there are also many domestic manufacturers have begun to focus on product development of the technology. The Xinhua Group R&D Center has already taken the lead in domestically implementing the EtherCAT technology productization, successfully developed the first domestic DCSTisNet-E1000 based on EtherCAT, and led the development of automated products based on EtherCAT technology in China.
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