Serial communication program based on Modbus protocol_RS485 bus system application
This paper explores the implementation of Modbus protocol, focusing on its two main transmission modes and the development of serial communication programs. It also provides a sample program written in Visual Basic (VB) to illustrate practical applications. Modbus is a widely used communication protocol that supports various physical layers such as RS-232, RS-422, RS-485, and Ethernet. It is commonly adopted in industrial automation systems, including PLCs, DCS, smart meters, and other control devices, to enable seamless data exchange between them. As a versatile and open protocol, Modbus allows controllers to communicate with each other over a network or directly through serial links. It defines a standardized message format that enables devices to request data, respond to queries, and handle errors efficiently. This structure ensures compatibility across different communication media and makes it a reliable choice for industrial environments. RS-485 is a standard for serial communication that operates in half-duplex mode and supports multi-point data transmission. Its typical network topology is a linear bus structure, where devices are connected in series. This configuration does not support ring or star topologies, making it ideal for long-distance communication in industrial settings. One of the key advantages of RS-485 is its ability to reject common-mode noise due to its differential signaling. This feature enhances signal integrity over long distances. Additionally, some transceivers can detect voltages as low as 200mV, allowing signals to travel over a kilometer. With enhanced input impedance, certain models support up to eight times more nodes on a single bus, making it highly scalable for complex systems. To make the concept more accessible, this example demonstrates a Modbus RTU communication setup. The hardware includes a computer and ten temperature and humidity sensors installed in different rooms, forming an RS-485 network. Each sensor is assigned a unique address from 01H to 0AH. When the computer sends a query, the corresponding sensor responds with a data frame containing 11 bytes of information, including temperature and humidity readings. This structured approach ensures accurate and efficient data exchange in real-world applications. Switch Cabinet Intelligent Operating Device Switch Cabinet Intelligent Operating Device,Wireless Temperature Measurement,Temperature Measuring Device,Wireless Temperature Measuring zhejiangjinyidianqiyouxiangongsi , https://www.jooeei.com
