Modbus is a serial communication protocol, a bus protocol released by Modicon Corporation (now owned by Schneider Electric) in 1979 to communicate with its programmable logic controller (PLC).

Several versions of the Modbus protocol exist for serial ports and Ethernet, the most common being: ModBus TCP, ModBus RTU, ModBus ASCII, and ModBus Plus.

What is it used for?

Modbus is an open protocol, which means manufacturers are free to build it into their devices without paying royalties. It has become a standard communication protocol in industry and is now the most common way of connecting industrial electronic equipment. It is widely used by many manufacturers in many industries. Modbus is commonly used to transmit signals from instrumentation and control equipment back to a main controller or data collection system, such as instruments and meters, intelligent high and low voltage electrical appliances, transmitters, programmable controllers, man-machine interfaces, frequency converters, field intelligent equipment and so on. Modbus is commonly used to connect supervisory computers and remote terminal units (RTUs) in supervisory control and data acquisition (SCADA) systems. Versions of the Modbus protocol exist for serial lines (Modbus RTU and Modbus ASCII) and Ethernet (Modbus TCP).

Generally speaking, Modbus is a protocol for industrial control, which has three characteristics: free use, easy to use and easy to change.

How does it work?

Modbus is transmitted over a serial line between devices. The simplest setup is to connect the serial ports of two devices (client and server) with one serial cable.

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