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PROTOCOLS · COMPARISON

Modbus RTU vs Modbus TCP: What Is the Difference?

Modbus RTU and Modbus TCP carry the same Modbus messages over different links. Modbus RTU sends compact binary frames over serial lines, usually RS-485, with a checksum on each frame. Modbus TCP wraps the messages in TCP/IP packets over Ethernet, normally on port 502. Gateways translate between them so serial devices can join Ethernet networks.

01

The Short Answer

Modbus RTU is still everywhere on equipment such as refrigeration controllers, energy meters and drives, because RS-485 is cheap, robust and runs long distances. Modbus TCP fits modern Ethernet networks and SCADA systems. An HMI or gateway with both serial and Ethernet ports can read RTU devices and present their data over TCP or to the cloud.

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    Modbus RTU Field devices on an RS-485 bus, often over long cable runs.
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    Modbus TCP Devices already on Ethernet, and links to SCADA and PLCs.
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    Both A gateway reads RTU devices and serves the data over TCP.
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    Plan the wiring RTU needs correct RS-485 termination and unique device IDs.
02

Why It Matters

Our Modbus FAQ covers the protocol, and our RS-485 FAQ explains the serial link. The supermarket HMI case study connects refrigeration over RS-485; see our industrial IoT gateways.