Modbus is a widely used communication protocol in the field of industrial automation and process control. It was developed by Modicon (now Schneider Electric) in the late 1970s and has since become an industry standard for connecting various devices, such as programmable logic controllers (PLCs), HMIs, sensors, and actuators.
Modbus is a master-slave protocol, meaning that one device, called the master, initiates communication and controls the exchange of data with one or more devices, called slaves. The protocol supports two primary modes of communication: Modbus RTU and Modbus TCP/IP.
- Modbus RTU: Modbus RTU is a serial communication protocol that typically uses RS-232 or RS-485 as the physical layer. It uses binary encoding and is based on a master-slave architecture. In Modbus RTU, messages are sent in a compact format, with each message consisting of a unique address for the slave device, the function code specifying the type of request or response, and the data being transmitted. Modbus RTU supports half-duplex communication, where data is transmitted in one direction at a time.
- Modbus TCP/IP: Modbus TCP/IP is a variant of the Modbus protocol that uses Ethernet as the physical layer. It allows Modbus messages to be encapsulated within TCP/IP packets, enabling communication over standard Ethernet networks. Modbus TCP/IP uses the client-server model, where a Modbus TCP/IP client initiates requests to Modbus TCP/IP servers. The protocol utilizes the IP addressing scheme and supports communication over LANs, WANs, and the internet.
Both Modbus RTU and Modbus TCP/IP support various function codes, which define the types of operations that can be performed. These function codes include reading and writing data registers, coils, discrete inputs, and holding registers, as well as diagnostic and control functions.
Modbus is known for its simplicity, reliability, and ease of implementation. It is an open protocol, allowing devices from different manufacturers to communicate seamlessly. Modbus has found widespread use in a wide range of industries, including manufacturing, energy, oil and gas, building automation, and more.