Modbus was introduced in 1979 by the company Modicon, a leader in the infant programmable logic controller (PLC) market. It was intended as the internal point-to-point communications protocol between Modicon PLCs and programming panels used to program the controllers. The protocol continues to thrive because it is easy to understand, and many engineers have "cut their protocol teeth" on Modbus. Besides, it is an open system and can be used royalty-free. It is not restricted to just industrial automation. Modbus can be found in numerous diverse automation industries including building automation.
There are two implementations of Modbus that are found today in industry. The first implementation is the traditional implementation of Modbus over a serial line called Modbus Serial. The second implementation is more modern with Modbus operating over a TCP/IP network called Modbus TCP.