modbus.JPGDeveloped by Modicon, the Modbus communication protocol is a messaging structure used to establish a master-slave or client-server communication between intelligent devices. The intelligent devices can be a PLC, HMI, PC, Distributed Control Systems (DCS), Supervisory Control and Data Acquisition Systems (SCADA) etc.


The Modbus protocol is not industry specific and can be used in a wide variety of industries such as factory automation, building automation, process control, oil & gas, traffic & parking, agriculture & irrigation, water & wastewater, pharmaceutical and medical, material handling, etc.


Modbus protocol can be operated via the following communication methods:


  • Modbus RTU or Modbus over serial This communication method or interface can be RS-485  RS-232RS-232 RS-422 and RS-423 Generally in this interface the Modbus devices would require the receive wire(RX the transmit wire(TX and the ground wire(GND to exchange data between the Modbus devices The interface can be either half duplex or full duplex Typically all intelligent devices can be configured for both half duplex and full duplex


  • Modbus™ TCP/IP – In this communication method, the Modbus data is wrapped around TCP/IP internet protocols and then the data is transmitted over standard internet. A standard RJ45 Ethernet port can be used to connect the various devices for data transfer. Modbus™ TCP/IP can be defined as an open standard implementation of Modbus on internet protocols.


  • EtherNet/IP™ - EtherNet/IP™ is an application layer/industrial protocol that is built on the standard TCP/IP stack, where TCP means transport control protocol and IP means internet protocol (IP). EtherNet/IP™ uses standard Ethernet hardware and operates over Ethernet using the common industrial protocols (CIP) – ControlNet & DeviceNet and the TCP/IP protocol stack. Although EtherNet/IP™ was developed by Rockwell Automation for its Allen Bradley line of controls, it is now considered an open standard and is managed by Open DeviceNet Vendors Association (ODVA).


To learn more about the Modbus Communication Protocol, please download the attached document by Honeywell's Sensing and Productivity Solutions called "Industrial Communication Protocols."