The Modbus communications protocol, introduced by Schneider Electric (Modicon) in 1979, has been proven to be extremely reliable and easy to implement. It has become a 'de facto' standard and the most widely used network protocol in the industrial manufacturing environment.

In a typical Modbus network, Modbus messages are sent over an RS232/RS485 asynchronous serial communication link (EIA standard); e.g., the Modbus-Master initiates a request for information and the Modbus-Slave device responds with the appropriate information sent back. General broadcasts of information are also possible, with no response needed. The two modes of communication within the Modbus network are 10-bit ASCII and 11-bit RTU.