Panasonic FP7 CPU Unit - 6 MODBUS TCP Master;Slave Communication; MODBUS TCP Format; Modbus Tcp

MODBUS TCP Master/Slave Communication
6.1 MODBUS TCP Format
6.1.1 MODBUS TCP
 Data structure for the MODBUS TCP format
• In MODBUS TCP, an MBAP header is attached to the function codes and data used in
MODBUS-RTU.
MBAP Header
7 bytes
Function
Code
1 byte
Data
n bytes
Transaction
Identifier
2 bytes
Protocol
Identifier
2 bytes
Length
2 bytes
Unit
Identifier
1 byte
MODBUS TCP format
MBAP header part
 Data contents
Fields Field name Description
MBAP
Header
Transaction Identifier Transaction identifier "00H" is entered.
Protocol Identifier Protocol identifier "00H" is entered.
Length Length
The length of the subsequent sending/receiving
message is entered.
Unit Identifier Unit identifier Station no. of the unit is entered. 0 - 247
Function code Function code
The same function name as that of MODBUS-
RTU is entered.
Data Data
Data that correspond to the function code are
entered.
KEY POINTS
• Function codes and data parts for MODBUS TCP are the same as those for
MODBUS-RTU. Note that, however, CRC check codes contained in the
MODBUS-RTU format are not included.
REFERENCE
For detailed specifications concerning MODBUS, please see the website
http://www.modbus.org/
.
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