Modbus follows a master–slave modbus communication model. In this setup, one device acts as the master (client) and initiates all communication, while other devices act as slaves (servers) and respond to requests. Slave devices cannot send data unless the master asks for it. This structure helps keep communication organized and prevents data collisions on the network.
Modbus is mainly used to transmit information such as sensor readings, control commands, and device status between industrial equipment. Typical applications include factory automation, building management systems, power monitoring, and process control in industries like oil and gas, water treatment, and manufacturing.
There are several versions of Modbus, each designed for different communication media. Modbus RTU and Modbus ASCII are used for serial communication, commonly over RS-232 or RS-485 connections. Modbus RTU is the most popular of the two because it is more compact and efficient. Modbus TCP, on the other hand, is used over Ethernet networks and is commonly found in modern industrial systems that rely on TCP/IP communication.
Data in Modbus is organized into registers, which store information such as input values, output states, and configuration settings. Each register has an address, and the master reads from or writes to these registers using standardized function codes. This structured approach makes it easy for devices from different manufacturers to communicate, as long as they support the Modbus protocol.
One of Modbus’s biggest advantages is its simplicity and openness. The protocol is easy to implement, well-documented, and does not require licensing fees. This has contributed to its long lifespan and widespread adoption. However, Modbus does have limitations. It lacks built-in security features like encryption and authentication, and its data speeds are relatively low compared to newer industrial protocols.