Modbus is an open standardized communication protocol that was founded by Modicon. Initially it was designed for the communication among PLCs in industrial applications but it also gained significance use in building automation domain for instance in HVAC systems, DDCs and room control.
In a nutshell, Modbus is an application layer messaging, protocol placed at OSI layer 7, for client/server communication between devices connected on different types of buses or networks. Modbus is a lightweight application layer protocol that facilitates different media. Modbus-TCP, a Modbus version based on TCP, is part of the fieldbus standard IEC 61158.
Modbus is transported using any of the following layers:
- TCP/IP
- RS232, RS422, RS485
- Modbus Plus, a token-passing network
- Other types of media like Fiber, Radio, Cellular
An example of a Modbus network is shown below:
Related: Features of Popular Fieldbuses used in Industrial Networking
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