What is the Modbus protocol?
Similar to CAN, Modbus is an older yet widely used industrial communication protocol allowing data exchange between devices in a network. Read on to learn more about the protocol, its functionality, and how you can apply Modbus to your day-to-day projects.
Figure 1: shows the general composition of request frames in Modbus RTU.
Written by: DigiKey Maker.io staff
uses the server’s internal register addresses to retrieve data from a device. Modbus is commonly used to transmit signals from instrumentation and control devices to a centralized controller. One example of this configuration could involve a system consisting of sensors measuring the temperature and vibrations of an electric motor in a factory crane. The collected data is then submitted to a computer for anomaly detection and to trigger safety measures when necessary. For such purposes, several
versions of the Modbus standard exist to support common physical communication standards, such as RS-232, RS-485, and Ethernet. Modbus object types and function codes The server devices store information and the client can either request register values or write values to registers. However, as Modbus is an older standard originally intended for use with industrial PLCs (Programmable Logic Controllers), the data tables defined by the protocol reflect this
A high-level view on the Modbus protocol Modbus is a serial communication protocol that primarily focuses on describing the message format, encoding, and addressing on a high level without dictating the underlying implementation on the physical layer. Each network comprises precisely one Modbus client and can accommodate anywhere from one to 247 Modbus servers. Each device on the bus has a unique address.
In Modbus RTU (Remote Terminal
Unit), the client is the only device capable of actively requesting data on the network. Conversely, the servers can supply data via their internal registers when instructed by the server. Each server has a unique address in the network, and the client
Figure 2: shows the general composition of some example responses in Modbus RTU.
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