1. Introduction The evolution of air conditioners, as traditional household appliances, towards intelligence, digitalization, and networking, achieving comprehensive digitalization, is an inevitable trend. Utilizing the internet, telephone networks, and industrial LANs, and employing advanced communication technologies, air conditioners within a specific region can be networked to achieve centralized control and monitoring, data acquisition, fault diagnosis, troubleshooting, and after-sales maintenance, both locally and remotely. This article introduces a networked air conditioning system based on the RS-485 fieldbus developed by Guangzhou Hualing Air Conditioning Equipment Co., Ltd. 2. Advantages of Networked Air Conditioning 2.1 It possesses all the cooling, heating, dehumidifying, and defrosting functions of a standalone air conditioner, enabling local operation. 2.2 It allows for remote on/off operation and operating mode setting. 2.3 It enables 24/7 automatic complementary rotation of multiple units in equipment rooms. 2.4 It allows for remote real-time operation status query and monitoring. 2.5 It can automatically feed back fault information to the monitoring center (maintenance center) and perform rapid remote fault diagnosis and troubleshooting. 3. Air Conditioning Network Bus Reliable and accurate data signal transmission is crucial in a network. This air conditioning network uses an RS-485 bus as the data transmission link to achieve half-duplex asynchronous communication. This is because, on the one hand, the RS-485 standard, as an electrical specification for multi-point, differential data transmission, has become one of the most widely used standard communication interfaces in the industry. This communication interface allows for multi-point, bidirectional communication over a simple pair of twisted pairs; each terminal only needs to be connected to the bus via the interface, enabling a true multi-point bus structure. Its noise suppression capabilities, data transmission rates, cable length, and reliability are unmatched by other standards. On the other hand, the RS-485 standard only specifies the electrical characteristics of the interface, without addressing connectors, cables, or protocols. Users can then establish their own higher-level communication protocols based on this. The following are the main features of the RS-485 interface: Balanced transmission multi-point communication Driver output voltage (with load): ≥|1.5V| Receiver input threshold: ±200mV -7V to +12V bus common mode range Maximum input current: 1.0mA/-0.8mA (12Vin/-7Vin) Maximum bus load: 32 unit loads (UL) Maximum transmission rate: 10Mbps Maximum cable length: 4000 feet 4. Network configuration The RS-485 bus does not support ring or star networks. If the incorrect connection method shown in Figure 1 (a, b, c) is used, although it can still work normally in some cases (such as short distance, low speed, low interference, etc.), as the communication distance increases or the communication rate increases, its adverse effects will become more and more serious, and even communication failure may occur. The main reason is that the signal is reflected at the end of each branch and superimposed on the original signal, causing a decrease in signal quality. Therefore, it is best to adopt a terminal-matched bus topology, using a single, continuous signal path bus to connect all nodes in series. The length of the lead-out line from the bus to each node should be as short as possible to minimize the impact of reflected signals on the bus signal. See the connection method of d, e, and f in Figure 1. Furthermore, the RS-485 standard does not specify the number of transceivers allowed on the bus, but it specifies a maximum bus load of 32 unit loads (UL). The maximum input current per unit load is 1.0mA/-0.8mA, equivalent to approximately 12kΩ. To expand the number of bus nodes, the scheme uses MAX487 devices with an input resistance of 48kΩ or higher (1/4UL), increasing the number of nodes to 128. A typical application of MAX487 is shown in Figure 2. 5. Composition of the Networked Air Conditioning System 5.1 Network System Application Block Diagram Figure 3 is the application block diagram of the networked air conditioning system. The entire system consists of three main parts: hardware, software, and transmission protocol. 5.2 Hardware Components and Functions 5.2.1 Air Conditioner Control Board (including MAX487 chip): Used to achieve automated, intelligent, and energy-saving control of the air conditioner. It receives and sends signals to and from the network via the MAX487 chip. Each device has a unique address code. 5.2.2 Network Cables and Connectors: Provide the physical link for network signal transmission. 5.2.3 Distributed Control Controller (DCSC): The DCSC is the core component of the network and the access device for the air conditioning network. It functions as a gateway, allowing access to each air conditioner for operation control and status monitoring. The DCSC can form a local area network with a local monitoring computer via an RS-232 bus. It can also use modulation and demodulation technology to call a remote master PC via telephone line for long-distance data exchange and real-time response to commands from the PC. The DCSC itself has an address code for network cascading expansion. 5.2.4 Personal Computer (PC): The PC is the active device responsible for collecting, analyzing, storing, tabulating, and printing data on the air conditioner's operating status. It also identifies and controls the air conditioner's address code in real-time or at set intervals according to user settings. 5.2.5 Modem: Used for remote monitoring, enabling remote monitoring computers to dial up to the internet and communicate with the distributed controller. 5.3 Software Composition and Design Methodology 5.3.1 Air Conditioner Control Software and Communication Software: The air conditioner control MCU uses a chip with a built-in UART port to improve asynchronous communication speed. The software design flow is shown in Figure 4. 5.3.2 Distributed Controller Software: The MCU uses a built-in UART port and connects to the air conditioner network via MAX487. It also uses modem technology to connect to the telephone network (interconnected network) via a modem chip. The software design flow is shown in Figure 5. 5.3.3 Local (Remote) PC Monitoring Software: The local (remote) PC network air conditioner monitoring software is developed using VC6.0 and is an interactive window application on the Windows 95/98 or Windows-NT platform. This is because software developed using VC6.0 runs quickly, has strong data processing capabilities, and a user-friendly interface. The software design flow is shown in Figure 6. 5.4 Transmission Protocol 5.4.1 The data format uses asynchronous serial communication, with the format: 1 start bit, 8 data bits, and 1 stop bit, as shown in Figure 7. The baud rate is selectable, with a default of 9600. 5.4.2 Communication Protocol 5.4.2.1 Since the 485 bus is an asynchronous half-duplex communication bus, the bus can only be in one state at any given time. Therefore, the system uses a master-slave response method. Normally, the air conditioner is in standby mode, and the PC coordinates the time-sharing of the bus. 5.4.2.2 The system uses data packet communication. Communication data is sent in frames and packets. Each packet consists of a preamble, length code, address code, command code, content, and checksum. The header code is used to synchronize each data packet; the length code is the total length of the data packet; the command code is the control command from the host to the air conditioner (or the air conditioner responding to the host); the address code is the local address of the air conditioner; the "content" is the various information in the data packet; and the checksum is the check mark for the data packet, which can use different methods such as parity check or checksum. 5.4.2.3 In the communication of the 487 chip, special attention should be paid to the software programming of the 487 control terminal DE. For reliable operation, an appropriate delay is required when switching the 485 bus state before sending and receiving data. Specifically, in the data transmission state, the control terminal is first set to "1", delayed for about 0.3ms, and then the valid data is sent. After one data packet is sent, another 0.3ms is delayed before the control terminal is set to "0". This processing ensures a stable working process during bus state switching. 6. Conclusion In today's increasingly competitive home appliance market, due to frequent price wars, the profitability of home appliance companies has declined significantly, and some companies have suffered losses. Market experience has shown that without new products incorporating advanced technologies, a relatively saturated home appliance market is difficult to revitalize. Therefore, the networking of home appliances is an inevitable trend of the times. This network solution has been proven through actual operation at the Guangzhou Hualing Air Conditioning Equipment Co., Ltd. factory and some external units, demonstrating excellent performance, safety, reliability, and the ability to achieve 24/7 real-time local or remote monitoring, showing promising application prospects.