Modbus is a data communications protocol commonly used for connecting industrial electronic devices. Modbus was originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs) in industrial applications. It is often used to connect a supervisory computer with a remote terminal unit (RTU) in Supervisory Control and Data Acquisition (SCADA) systems. 

Compared to other standards, Modbus is relatively easy to deploy and maintain, and places few restrictions on the format of the data to be transmitted. Its popularity is boosted by the fact that it is openly published and royalty-free.  Modbus uses the RS485 or Ethernet as its wiring type, and supports communication to and from multiple devices connected to the same cable or Ethernet network.

RS485 – Recommended Standard-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications. 
 

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