Port :502Modbus

Modbus is an open, serial communications protocol originally published by Modicon in 1979 for use with its programmable logic controllers (PLCs). Due to its simplicity and strong adoption, it became a de facto standard communication protocol in industrial environments, supporting both serial (RTU and ASCII) and Ethernet (Modbus TCP) implementations. It allows for communication over TCP port 502, the well-known port assigned for Ethernet implementations.

Modbus operates in a master/slave or client/server architecture. A single master/client issues requests to read or write data on one or multiple slave/server devices, which respond only to requests and never initiate communication. Data is structured as registers and coils, which correspond to analog values and digital inputs/outputs respectively, making it flexible for monitoring and controlling diverse devices.

In Ethernet-based setups, Modbus TCP encapsulates Modbus frames in TCP packets, leveraging IP networks for increased range and connectivity. The protocol remains widely adopted in industrial automation (e.g., SCADA systems), building management, and energy management systems due to its ease of use and implementation across many vendors.