Signals and PLC · Glossary
What is Modbus TCP?
Modbus over EthernetSignals and PLC
Modbus TCP carries Modbus messages over Ethernet and TCP/IP, normally on port 502.
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Modbus TCP Explained
The message keeps the same function codes and data, wrapped in a header with a transaction ID. TCP handles error checking, so there is no CRC.
Gateways convert between Modbus TCP and RTU so Ethernet systems can reach serial devices.
Modbus TCP: Typical Values
| TCP port | 502 |
| Unit identifier | used to address devices behind a gateway |
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Calculators for Modbus TCP
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Frequently Asked Questions
What is Modbus TCP?
Modbus TCP carries Modbus messages over Ethernet and TCP/IP, normally on port 502.
Is Modbus TCP faster than RTU?
Usually, because Ethernet is far faster, but device response time often limits throughput.
How are floats sent?
As two 16 bit registers in IEEE 754 format; word order varies by device.
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Modbus RTU vs Modbus TCP
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