Developed by Modicon company back in 1979, Modbus is a data communications protocol that was originally designed to be used with Modicon’s programmable logic controllers (PLCs) and over the time became a de facto standard communication protocol for industrial electronic devices. Today, Modbus can be seen as a common way of connecting a plant/system supervisory computer with a remote terminal unit (RTU) in supervisory control and aata acquisition (SCADA) systems in industrial automation solutions.
Thanks to our flexible input APIs, Clarify can be easily connected to Modbus solutions, providing a cost-efficient and simple way of getting value from the time series data collected and used by industrial control devices.
Modicon company is known as the creator of the first programmable logic controller (PLC) in the United States in 1968.
Modicon was formed in 1968 by Bedford Associates Group, which consisted of four engineers—Dick Morley, Tom Boissevain, George Schwenk, and Jonas Landau—who had just invented the Modular Digital Controller. The invention was a result of Bedford Associates winning a proposal for an electronic replacement for hard-wired relay systems requested by GM Hydramatic (the automatic transmission division of General Motors).
After calling their invention of a new controller, Bedford Associates decided to start a new company, named Modicon, which stood for MOdular DIgital CONtroller. The new company was established to focus on developing, manufacturing, selling, and servicing this new product.
Features that made original Modicon digital controllers a market success were their rugged design, modular inputs/outputs (I/0), which made it easy to connect a wide range of field devices, and a new programming language, called Ladder Logic. The new language simulated the behavior of the relay contacts and coils that were already familiar to industrial process engineers.
The term PLC (Programmable Logic Controller), describing the devices of this kind, was coined several years later, in 1971, by Allen-Bradley, another legendary brand of industrial automation equipment.
In 1977, Modicon was acquired by Gould Electronics who subsequently sold it to AEG in 1989. In 1994, AEG and Groupe Schneider merged to form AEG Schneider Automation, which became solely owned by Groupe Schneider in 1996. Groupe Schneider was renamed as Schneider Electric in 1999.
In 2004, Schneider Electric gave up its ownership of Modbus and transferred it to Modbus Organization, an association of users and suppliers of Modbus-compliant devices, created for the promotion and development of Modbus protocol.
The Modbus Organization, headquartered in Massachusetts, is a nonprofit, membership-based trade association of users and suppliers of Modbus-based automation devices. The organization members include automation equipment suppliers, system integrators, end users, open source developers, educators and other parties. It was formed to support the Modbus protocol, drive its adoption, provide information and tools for individuals and companies using Modbus, and to address architectures for distributed automation systems across multiple market segments.
The Modbus Organization maintains the modbus.org website with information about Modbus, its applications and certifications required to simplify the implementation of this protocol. The organization also engages in various activities related to the maintenance and proliferation of Modbus, including maintaining and evolving a conformance testing program to insure greater interoperability of Modbus devices, as well as educational and promotional efforts.
Originally designed to be used with Modicon’s newly invented Modular Digital Controller and published as an open and royalty-free protocol, Modbus soon became a de facto standard communication protocol in industrial environments.
Modbus gained popularity in industrial applications due to its simplicity and lack of restrictions, which made it easy to deploy and maintain Modbus communication compared to other standards. When it comes to the transport layer, Modbus supports Ethernet, the Internet protocol suite, and character serial communication lines. The protocol also allows the communication of multiple devices connected to the same Ethernet network or a cable.
Today, Modbus is commonly used to connect a plant/system supervisory computer with a remote terminal unit (RTU) in supervisory control and aata acquisition (SCADA) systems in the electric power and other industries. There are multiple versions of the protocol for different kinds of connections. They include Modbus RTU (Remote Terminal Unit), Modbus ASCII, Modbus TCP/IP, Modbus over UDP, and other variants.
Interestingly, there is also the Modbus Plus protocol, which is not a version of Modbus but a separate protocol that involves token passing. The rights to Modbus Plus belong to Schneider Electric.
Modbus Security protocol
In 2018, the Modbus Organization announced the publication of the Modbus Security protocol. The new protocol provides robust protection through the blending of Transport Layer Security (TLS) with the traditional Modbus protocol. TLS encapsulates Modbus packets to provide both authentication and message-integrity protection. The new protocol leverages X.509v3 digital certificates for authentication of the Server and Client.
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