Abstract: LonWorks bus technology is a control network technology. Its basic control unit—the NERUN chip—possesses both communication and control functions, embedding the communication protocol of all seven layers of services defined by the OSI reference model, and has the advantages of openness and interoperability. This paper focuses on the system expansion method based on the Neuron chip (Neuron TMPN 3150), proposing three different system expansion models. Keywords: LonWorks bus, interface, system expansion. LonWorks technology is a practical Open Systems Interconnection (OSI) model and is currently the only communication protocol that can provide all seven layers of services defined by the OSI reference model. The openness and interoperability design principles advocated by LonWorks technology provide a good model for the design and development of fieldbuses. Although LonWorks technology has only been around for a few years, its successful application in many fields demonstrates its vitality. The neuron chip is the core controller of LonWorks bus technology and the basic unit of a LonWorks system. Besides its strong bus communication and control capabilities, it can also perform various data processing functions. By rationally utilizing the internal resources and powerful external expansion capabilities of the neuron chip, a simple, stable, and reliable distributed control system can be easily constructed. This is especially important for large-scale distributed control systems. 1. Characteristics of LonWorks Technology Many control systems today employ a distributed system architecture. In this architecture, control is implemented locally or directly between local controllers without the need for a master controller. There is no master-slave relationship between controllers; they collaborate to form a large control system. In this structure, system reliability is distributed across various components, preventing the failure of one component from paralyzing the entire system and improving overall system reliability. LonWorks technology is a general-purpose control network technology widely used in Sensor Bus, Device Bus, and Field Bus. It supports various topologies, including bus, star, and ring, and also supports the mixing of these structures. LonWorks technology can use various communication media, from low-end twisted pair to high-end fiber optics, from power line carrier to infrared, wireless transmission, etc., and can be used in the same network. Compared with general fieldbus, LonWorks technology has many advantages: (1) It adopts the LonTalk communication protocol, which follows the Open Systems Interconnection (OSI) model defined by the International Organization for Standardization (ISO), and is the only communication protocol that can provide all seven layers of services defined by the OSI reference model. (2) The neuron chip can realize communication and field control functions. It contains three 8-bit CPUs, two of which are used to realize the communication control of the LonWorks network, and one is used to realize the local control function. (3) It uses Predictive P-Persistant CSMA (Predictive Time Slot-Carrier Detection Multiple Access) to detect bus conflicts, ensuring that the network will not be paralyzed when the network load is heavy. (4) The network communication is implemented using an object-oriented design method. The network variables simplify the design of the network communication to the setting of parameters, which greatly improves the reliability of the communication. (5) The short packet structure is adopted to improve the anti-interference ability of the communication and improve the real-time performance of the communication. Variable length data frames are adopted, and the length of each frame is 0-228 bytes. (6) There are two communication speeds: 78KBps and 1.25MBps. (7) The communication distance is 130m-2700m. (8) The number of nodes on the same network can reach 32,000. 2. Distributed control system architecture based on neural network chip The control system using LonWorks technology is a fully distributed control system. Each control unit on the bus is a peer control node. The LonWorks system can be divided into domains and subnets through routers. A subnet can have up to 62 nodes, and a domain can have up to 32,000 nodes. A node can also belong to two different domains at the same time. Data communication between the two domains can be realized through the node. This method can be used to expand the total number of nodes on the network. For a system with a small number of nodes or an application system with high real-time requirements, a single or two-level LonWorks control network can be used; for systems that require remote monitoring or a large amount of data management, a LonWorks network can be used between adjacent nodes, and remote nodes can be connected through an i.Lon1000 router to achieve seamless integration between the LonWorks network and the TCP/IP network, and remote monitoring of the system can be achieved through the Internet. Therefore, there are two different architectures: (1) a system composed of a LonWorks network bus. (2) a system with a LonWorks bus at the bottom layer and an Internet network at the top layer. [align=center] [/align] 3. System Expansion Methods for LonWorks Controller Chips When designing a control system using a neuron chip, depending on the complexity of the system, the following three different IO expansion methods can be considered: (1) Expanding the neuron chip through 11 I/O pins This method is the smallest and simplest system, requiring no additional external circuitry. It is suitable for control systems with few control quantities at each node. It fully utilizes the 11 I/O pins of the neuron chip itself to expand the system. The functions of these 11 pins are very flexible and can be defined in 34 different input/output modes, such as: It can be defined as input/output mode by byte/half-word/bit. It can also be defined as a serial input/output port. It can be defined as a Wiegand code input port for reading and writing magnetic cards. It can also modulate the output pulse width for driving stepper motors. It can be defined as the input port of a counter, etc. These flexible and varied usage methods bring great convenience to industrial control. If there are not many control parameters, this method can be used as much as possible, which will make the control system very simple. (2) Neuron Chip with I/O Address Expansion Interface: If the 11 I/O pins of the neuron chip itself cannot meet our control requirements, we can consider using a structure that expands the external interface through I/O addresses. The neuron chip provides us with 2K of I/O space, which can be used to expand our I/O interface and realize the interconnection between the system and external devices. (3) Neuron Chip with Peripheral Microprocessor (Microcontroller/DSP) for I/O Expansion: In some application systems, the control parameters are relatively complex. A front-end processor can be used, with a microcontroller or DSP chip specifically handling complex control tasks. They exchange data with the neuron chip through serial or parallel ports. In this case, the neuron chip mainly implements communication processing functions, while most of the control and data calculation work is completed by the front-end processor. In the process of developing an intelligent community home controller, because the functions of each node are relatively complex, we adopted this structure to alleviate the contradiction of the internal resource shortage of the LonWorks controller chip and meet the requirements of each node for complex tasks. This approach was not actually the original design intent of the LonWorks system. When developing LonWorks technology, Echelon emphasized the distributed nature of the system, aiming to simplify the function of each node as much as possible, with the entire network coordinating the work of a large system. However, due to factors such as price, it is currently impossible to make a single node so simple. Therefore, a compromise expansion method has to be adopted to reduce the production cost of each node. In Figure 3, the TP/FT-10 module is a LonWorks transceiver. The Neuron TMPN 3150 neural chip can use this transceiver (TP/FT-10) module to convert TTL signals to LonWorks signals. 4. Software Implementation Method The LonWorks system supports C language programming, called Neuron-C, which is a subset of standard C and extends it with a WHEN statement as an event-driven condition. Neuron-C is a multi-task scheduler that can describe multiple parallel events through multiple WHEN statements and control the priority of processing these events. Once you understand the basic C programming methods, you can quickly master Neuron-C software programming. In the LonWorks system, data communication is completed in the presentation layer. Data in the presentation layer is called network variables, which can be a single data item or a data structure. Using network variables for data communication simplifies the programming of distributed applications. Programmers do not need to handle message buffers or the addresses of sending and receiving nodes, choose message processing methods, or worry about low-level details. They only need to reassign the network variable, and the value of the network variable will be automatically sent to the specified node. The LonTalk communication protocol provides four basic message service types: Acknowledge, Unacknowledge, Request/Response, and Unacknowledge Repeated. These methods can meet the needs of applications with different security requirements. 5. Conclusion Although LonWorks technology is relatively new, its development has been exceptionally rapid due to its significant advantages in industrial control. Currently, thousands of manufacturers worldwide are developing or using this technology, spanning industries such as automation control, intelligent buildings, energy, and transportation. In recent years, China has also made rapid progress in this area. For example, in the field of intelligent buildings, manufacturers who previously used RS-485 communication are now widely adopting LonWorks buses. It is estimated that LonWorks technology will see even greater development in the coming years. References: 1. Neuron chip TMPN3150 Reference Manual, Toshiba Company, 2000.2; 2. Open System Design Guide, Echelon CO., 1999.11