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Topics

Fast Communication between Automation and Field Devices: MODBUS

The MODBUS protocol is a communication protocol based on master/slave or client/server architecture. The primary purpose of the protocol is facilitating reliable, fast communication between automation and field devices.

Advantages with MODBUS:

  • Uniform data exchange compliant with standards
  • Very fast data transmission
  • Independent of technology and manufacturer

MODBUS Explained Simply

The well-established MODBUS protocol has become the de facto standard. It extends the MODBUS protocol familiar since 1979 for programmable logic controllers. The advantage: MODBUS is a streamlined protocol that ensures ultra-fast ETHERNET data transmission. A manufacturer-independent data structure also permits communication between devices from different manufacturers.

MODBUS in Action

MODBUS enables connecting a master (e.g., a PC) and several slaves (e.g., measurement and control systems). There are two versions: One for the serial interface (RS-232 and RS-485) and one for ETHERNET.

The following data transmission operating modes are distinguished:

  • MODBUS TCP: ETHERNET TCP/IP communication based on client/server model
  • MODBUS RTU: Asynchronous, serial transmission via RS-232 or RS-485
  • MODBUS ASCII: Similar to RTU protocol except for a different data format; relatively rarely used