What is Modbus?
Modbus is a serial communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.
Versions of the Modbus protocol exist for serial port and for Ethernet and other protocols that support the Internet protocol suite. There are many variants of Modbus protocols: Modbus RTU , Modbus ASCII, Modbus TCP/IP or Modbus TCP, Modbus over TCP/IP or Modbus over TCP or Modbus RTU/IP, etc.