Abstract: This paper analyzes the advantages of embedded industrial Ethernet control technology over fieldbus, proposes a complete network control scheme, and specifically analyzes the composition and development details of the low-level field control module, with the development of the TCP/IP protocol being the focus. The scheme has a simple structure, flexible control, and can realize real-time transmission and true sharing of enterprise information. Keywords: Fieldbus; Industrial Ethernet; Embedded; Node control module 1 Introduction In the field of industrial automation, a large number of intelligent devices can be connected to the Internet through various means, exchanging information and data with each other through the network, realizing the functional autonomy of intelligent field devices, the high degree of system architecture distribution, and the integration of supervision and control. Fieldbus is a new technology that has developed in response to this situation. The emergence of fieldbus marks the beginning of a new era in the field of industrial control technology. The development of this technology has played a huge role in promoting the realization of equipment-oriented automation systems. Compared with traditional distributed control systems (DCS), it has advantages such as full openness, full distribution, and interoperability, but it still has great limitations, mainly in the following aspects: (1) The computing power and information processing capabilities of current field instruments and equipment are low. Complex control functions are still concentrated on a single control computer, which cannot achieve full distributed control and results in concentrated risks. (2) Fieldbus is only a component of the system and is located at the bottom layer of the system, which is insufficient to achieve a fully open system structure. The system architecture is vertically combined, and there are bottlenecks in data communication. (3) The IEC61158 standard includes eight types of fieldbuses, which are quite different from each other and cannot achieve interoperability. Connecting them is difficult. (4) All controllers in the system operate independently and perform independent data processing, making it difficult to share all information, resulting in unsatisfactory real-time performance. The above description shows that traditional classic PLC and fieldbus technologies are no longer suitable for this requirement. Even technologies such as industrial PCs and OPCs, as long as they are embedded in traditional system structures, can only make some marginal improvements to the system's functions. Therefore, in order to reduce the heavy programming work and simplify the system, it is necessary to change the structure of the system. With the continuous leapfrog development of information technology, a control strategy that can make up for the defects of fieldbus and realize the unified, efficient and real-time control of the whole system will inevitably emerge in the field of industrial control. Industrial Ethernet is a control technology that has developed rapidly to meet this need. Among all network technologies, Ethernet technology is the most ideal choice to date. It can meet all the following requirements: (1) It fully considers the needs of future development and has a high transmission rate, currently reaching 100 Mb/s. (2) High transmission security and reliability, determinism of hub technology. (3) The application of hub does not need to consider network expansion. (4) It has established a standard: a new industrial control bus standard. (5) It connects with IT and applies the "world standard" TCP/IP technology. (6) Random network access technology in the whole network. Ethernet is a technology for computers to access local area networks. Due to the significant increase in Ethernet transmission speed, the industrialization of physical layer standards, the formation of Ethernet hub technology, and the emergence of Gigabit Ethernet and collision-free full-duplex fiber optic technologies, this advanced network technology has been pushed into industrial control networks, which were previously considered unsuitable, thus forming industrial Ethernet technology. Compared with current fieldbus-based control networks, industrial Ethernet-based control networks offer a low-cost (many commercial Ethernet chipsets and technologies can be borrowed) and high-performance control network solution. 2 Solution Analysis 2.1 Embedded Industrial Ethernet Control System Solution Design The control system network is divided into three layers: information layer, control layer, and device layer (sensing/execution layer). Traditional control systems mostly use Ethernet in the information layer, while different fieldbuses or other dedicated networks are generally used in the control and device layers. Currently, almost all PLC and remote I/O vendors offer products with Ethernet interfaces that support TCP/IP. With the adoption of an Ethernet architecture, the location of the controller can also break through the limitations of traditional network architectures, and can be located in the field or in a central control room. Currently, controllers and even remote I/O support Ethernet functionality more and more. Some controllers and remote I/O modules have integrated Web servers, allowing information layer users to directly obtain the current status values ​​of controllers and remote I/O modules just like control layer users. In this scheme, the network control system is divided into three parts: (1) Field device layer, including embedded node control modules and field workstations. The former mainly completes the acquisition of field data, processing and storage of front-end data, and communication with the upper layer through the Internet interface. The control module can realize server functions, and the information layer can access it through Web browsing (supporting point-to-multipoint communication). The latter is mainly responsible for some auxiliary and monitoring tasks, such as field data transmission, historical data processing, report output, etc. (2) Internal information layer is mainly composed of the enterprise's internal Ethernet. It mainly completes the information collection and release of the entire system, that is, by accessing the Web server in the field node control module, the data of all monitoring nodes under monitoring is concentrated in the local area network server through the HUB hub, and managed and stored in a unified manner, and released to the upper management department through Web browsing. (3) Internet Network Layer This layer connects various local area networks of the enterprise through switches and routers to complete the global release of information. Departments located in the office can intuitively see the on-site work situation, production plan completion status and equipment working status, etc. Even if they are thousands of miles away, they can grasp the operation of the enterprise (company) anytime and anywhere, making remote office a reality. The industrial Ethernet control system scheme is shown in Figure 1. 2.2 Implementation of Embedded Interface Control Module In the industrial Ethernet architecture, Ethernet serves as the system bus connecting intelligent control modules, and there is no difference between internal and external data communication. Hub technology is integrated into each controller, separating internal communication from external communication by allocating address space. The integration of hub technology and underlying protocols ensures the determinism, compatibility and integrity of Ethernet. At present, the protocols at the transport layer and network layer have been basically unified, and TCP/IP has become the standard network protocol, which is the "central hub" for the normal operation of Ethernet. A key link in industrial Ethernet technology is to implement the TCP/IP network communication protocol in the field-level node control module (such as remote I/O module), that is, to establish a protocol stack. With the rapid development of electronics and information technology, embedding the TCP/IP protocol into node modules through software or hardware has become possible. The software approach embeds TCP/IP into the microprocessor's ROM, while the hardware approach designs embedded processors and ASIC chips directly as network interfaces. This solution uses a RISC-based microcontroller with on-chip Flash program memory, enabling in-system programming and debugging. Due to the CPU's parallel pipeline and single-clock-cycle instruction set, the instruction execution speed can reach 100 MI/s under a 100 MHz crystal oscillator. All I/O pins can be flexibly configured through programming. Based on these features, virtual peripheral functionality can be implemented: the CPU directly drives ordinary I/O ports to achieve hardware peripheral functions (such as UART, I2C, SPI, CallerID, FSK, etc.) by executing virtual software modules. Most notably, this feature allows the implementation of popular Internet protocol stacks such as HTTP, SMTP, POP3, TCP, UDP, ICMP, IP, and PPP. The node module is implemented in a multi-tasking manner. While the microcontroller is performing data acquisition or completing I/O control tasks, it can also complete Internet protocol processing. At the application layer, any one of HTTP, SMTP, and POP3 can be selected as the communication protocol between the microcontroller system and the Internet remote management terminal; or other programs based on TCP and UDP protocols can be developed as application layer software. Using an Ethernet control chip, data packets can be sent to the Ethernet and accessed through the Ethernet to the Internet, realizing a true embedded TCP/IP device. Figure 2 is a schematic diagram of the control module structure. RJ45 is the interface between this system and the local area network. The data flow is as follows: the request information comes from the local area network, is sent to the network card control chip through RJ45, and after processing, the data packet of 05 is sent to the microcontroller protocol stack. The protocol stack parses the data packet to obtain the original request information. The request information is then processed by the microcontroller to generate reply information. The process of replying information to the local area network is exactly the opposite of the above. Features of the interface control module: (1) It does not rely on PCs or high-end microcontrollers, truly realizing the direct access of the 8-bit microcontroller system to the Internet, and the entire system is completely self-sufficient. (2) Fewer peripheral components are used, resulting in lower system cost. (3) Supports IP, TCP, UDP, ICMP, HTTP, and SMTP protocols. (4) The system provides a 10/100 Base-T network interface, directly supporting the Ethernet IEEE 802.3 protocol. (5) Through the system's built-in RS232 serial interface, which supports Web page downloading, the system can display and control monitoring point data in real time and dynamically. 2.3 Ethernet Communication Protocol Development Ethernet is designed according to the requirements of a local area network. The Ethernet standard (IEEE 802.3) defines the physical layer and data link layer of the OSI reference model. The physical layer defines cable types, connectors, and signal levels; the data link layer defines frame formats, error control methods, channel allocation methods, etc. However, Ethernet cannot complete the functions of layers 3 and above of the OSI model. In this sense, it does not belong to a complete network protocol. The key to solving the problem lies in how to implement the network layer, transport layer, and application layer of the OSI model based on the existing protocol. The implementation principle of the network protocol stack is shown in Figure 3. The software protocol stacks in Figure 3 are all written in microcontroller language and stored in the flash program memory of the microcontroller. Different manufacturers at home and abroad have launched different industrial Ethernet protocols for their Ethernet products. In general, protocol development focuses on the following three aspects: (1) Network layer protocol The network layer mainly handles the activities of packets in the network, such as packet selection and route determination. It includes: IP protocol (Internet Protocol), ICMP protocol (Internet Control Message Protocol) and IGMP protocol (Internet Group Management Protocol). IP protocol is the main application object. All data in the Internet is transmitted in IP packet format. Its biggest feature is that it provides unreliable and connectionless datagram transmission service. In the development of the protocol stack in the embedded control module, the implementation of the IP layer is to package the message to be sent into IP, that is, add IP packet header to make it conform to the format of IP packet and send it to the physical layer; and to unpack the data packets received from the physical layer into IP, that is, remove the packet header and send it to the TCP layer. (2) Transport layer protocol TCP provides a connection-oriented, reliable byte stream transmission service. Once a datagram is corrupted or lost, it is retransmitted by TCP. In the embedded module protocol stack, the TCP layer is implemented through the provided TCP API (Application Programming Interface). (3) Application layer protocol HTTP is the protocol on WWW. When a user wants to browse a webpage on the server, an HTTP request is sent from the user's browser to the HTTP server. The server responds to the request and sends the specified webpage back, and the user sees the webpage. Because the HTTP layer is below the TCP layer, that is, HTTP uses TCP as its transport protocol, so the above two TCP connections are also used by the WebServer. Naturally, the send and receive functions of the TCP API are also used to implement the WebServer's request and response commands to complete data transmission. In the control module, the HTTP protocol can be used to construct the Web server, the SMTP protocol can be used to construct the mail service client, the PPP protocol can be used to construct the point-to-point system, and finally a C/S model can be established. All server resources are stored in external memory (E2PROM), and its capacity determines the size of the WebServer's resource files. HTTP uses a Uniform Resource Locator to specify the network resources (such as HTML, text documents, images, Java scripts, Java applets, PDF documents, etc.) returned to the client. Any type of Web server in the network can interact with it to realize remote and real-time control. 2.4 Development of System Application Platform The development of industrial control application software is mainly based on a B/S network architecture. The control layer collects field data information and establishes a Web resource server through intelligent node modules. Clients only need a browser to read the data in real time and transmit control commands. The focus of this application system is the development of the underlying server. Meanwhile, the system's monitoring software adopts a networked design, possessing good scalability and interconnectivity, with functions such as centralized parameter display and real-time data query, as well as special functions brought about by the networking of all devices, such as automatic switching of control modules, network fault detection, and resource sharing. 3 Conclusion The rapid development of network technology has profoundly influenced the transformation of industrial automation technology. Embedded industrial Ethernet, a highly open, flexible, convenient, and powerful new type of industrial control network, will connect the field equipment layer, control layer, and management layer of an enterprise with very high efficiency, forming an enterprise information system based on network integrated automation. It will inevitably permeate all aspects of manufacturing industries such as machinery manufacturing, automobile manufacturing, semiconductor manufacturing, and petrochemicals, and will also be widely used in building automation, power system monitoring, robot control, textile packaging, printing, and all other fields requiring digital information exchange and integration. Therefore, using industrial Ethernet as a brand-new "fieldbus" is an inevitable choice for future industrial control networks. 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