Modbus RTU Modbus RTU Basics Modbus RTU the Protocol

Modbus

  • Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers (PLCs)
  • Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems
  • Modbus RTU is an open, serial (RS-232 or RS-485) protocol derived from the client/server architecture
  • Modbus RTU is a compact, binary representation of the data

Modbus RTU is commonly found in:

  • Building Management Systems (BMS)
  • Industrial Automation Sytems (IAS)

Benefits Over Other Protocols

  • Modbus RTU is easier to implement than newer protocols
  • Modbus RTU is already commonly found in most automation systems
  • Modbus RTU requires much less memory for storage than BACnet or Ethernet/IP
    • Modbus RTU requires 2Kb on an 8-bit CPU whereas BACnet or Ethernet/IP may require 30 – 100Kb of memory.

Drawbacks

  • Limited use as a device bus
  • Limited diagnostic capabilities for device applications
  • Separate power required for device operations
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