Modbus tcp /ip support, Overview – Comtrol ES7528 User Manual
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RocketLinx ES7528 User Guide: 2000509 Rev. C
ModBus TCP /IP Support - 213
ModBus TCP /IP Support
This section provides the following information:
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CLI Commands for Modbus TCP/IP
Overview
The ES7528 supports Modbus TCP/IP communications through the CLI, which does not support Modbus
ASCII or Modbus RTU. This functionality is not available on a web user interface page.
Modbus TCP/IP is commonly used to communicate over TCP/IP networks, connecting over Port 502. Modbus
TCP/IP is used in industrial automatic communications systems and has become a standard protocol for
industrial communications to transfer data to analog I/O devices or PLC systems.
Modbus TCP/IP defines a simple protocol data unit independent of the underlying data link layer. The Modbus
TCP/IP packet includes three parts:
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MBAP header is used in the TCP/IP header to identify the Modbus application data unit. The MBAP
header also includes a unit identifier to recognize and communicate between multiple independent
Modbus end units.
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Function code
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Data payload
Modbus devices communicate using a master (client) /slave (server) architecture, only one device can initiate
a transaction and the others respond to the master/client. The other devices (slave/server) respond by
supplying the requested data to the master/client, or by taking the action requested in the query. The slave/
server can be any peripheral device that processes information and sends the output data to the master using
Modbus TCP/IP protocol.