Modbus Server - LS ELECTRIC XGT Series User Manual

7.2 Modbus Server

It is used when another device or upper PC (HMI) operates as Modbus master.
Overview
7.2.1
The Modbus TCP/IP protocol is the function to read and write data using the function code. The Modbus TCP/IP frame
consists of MAC, Header, TCP Header and Modbus ADU for the Ethernet communication.
- ADU: Application data unit
- PDU: Protocol data unit
- MBAP: Modbus application protocol
(1) Frame structure
1) Modbus TCP/ IP Server Packet Structure Using Ethernet
MAC IP Header
2) Modbus TCP/IP server frame structure
MABP Header
MABP Header
Transaction Identifier
Ethernet Request / Response Frame
TCP Header
MODBUS TCP/IP ADU
Function Code
Protocol Identifier
MODBUS TCP/IP ADU
MODBUS TCP/IP ADU
Data
PDU
Length Unit Identifier
Chapter 7 server service
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