We received this question from a student at a recent IIoT Learning Class. We found it particularly prescient given the latest discussions going on around Industry 4.0. The question is technically sound and indicates a thorough understanding of the technology’s functionality—but perhaps not its purpose.
The answer, however, is much deeper, and accounts for what lies ahead in terms of industrial Protocols.
What is Modbus protocol?
Modbus Protocol is a messaging structure developed by Modicon in 1979. It is used to establish master-slave/client-server communication between intelligent devices. It is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment. It has been implemented by hundreds of vendors on thousands of different devices to transfer discrete/analog I/O and register data between control devices. It’s a lingua franca or common denominator between different manufacturers. One report called it the “de facto standard in multi-vendor integration”. Industry analysts have reported over 7 million Modbus nodes in North America and Europe alone.
Where Modbus is used?
Modbus is used in multiple master-slave applications to monitor and program devices; to communicate between intelligent devices, sensors and instruments; to monitor field devices using PCs and HMIs. Modbus is also an ideal protocol for RTU applications, where wireless communication is required. For this reason, it is used in innumerable gas and oil and substation applications. But Modbus is not only an industrial protocol. Building, infrastructure, transportation and energy applications also make use of its benefits.
The right tool for the right task
When it comes to choosing a network for your device, Modbus TCP/IP offers several significant advantages:
- Simplicity:Modbus TCP/IP simply takes the Modbus instruction set and wraps TCP/IP around it. If you already have a Modbus driver and you understand Ethernet and TCP/IP sockets, you can have a driver up and running and talking to a PC in a few hours. Development costs are exceptionally low. Minimum hardware is required, and development is easy under any operating system.
- Standard Ethernet:There are no exotic chipsets required and you can use standard PC Ethernet cards to talk to your newly implemented device. As the cost of Ethernet falls, you benefit from the price reduction of the hardware, and as the performance improves from 10 to 100 Mb and soon to 1 Gb, your technology moves with it, protecting your investment. You are no longer tied to one vendor for support, but benefit from the thousands of developers out there who are making Ethernet and the Internet the networking tools of the future. This effort has been complemented opportunely with the assignment of the well-known Ethernet port 502 for the Modbus TCP/IP protocol.
- Open:The Modbus protocol was transferred from Schneider Electric to the Modbus Organization in April 2004, signalling a commitment to openness. The specification is available free of charge for download, and there are no subsequent licensing fees required for using Modbus or Modbus TCP/IP protocols. Additional sample code, implementation examples, and diagnostics are available on the Modbus TCP toolkit, a free benefit to Modbus Organization members and available for purchase by non-members
Availability of many devices: Interoperability among different vendors’ devices and compatibility with a large installed base of Modbus-compatible devices makes Modbus an excellent choice.