Mitsubishi QJ71MT91 User Manual

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MELSEC-Q
4 MODBUS
R
STANDARD FUNCTIONS
4.2 Frame Specifications
The frame specifications of MODBUS
R
/TCP are indicated below.
Application dataIP header TCP header
FCS
(Error check)
Ethernet frame
(MODBUS /TCP application data unit)
R
R
MBAP header
(MODBUS application header)
R
PDU
(Protocol data unit)
Protocol ID Module ID Function code
Data
(Message length)
Ethernet
header
MODBUS /TCP ADU
Message
length
Transaction
ID
Area Name Area Size Description
Transaction ID 2 bytes
Used by the master for matching of the response
message from the slave.
Protocol ID 2 bytes
Indicates the protocol of the PDU (protocol data
unit).
Stores 0 in the case of MODBUS
R
/TCP.
Message length 2 bytes
Stores the message size in byte unit.
The message length after this field is stored. (See
the above figure.)
MBAP header
(MODBUS
R
application
header)
Module ID 1 byte
Used to specify the slave connected to the other
line, e.g. MODBUS
R
serial protocol.
Function code 1 byte
The master specifies the processing to be performed
for the slave.
PDU
(Protocol data unit)
Data 1 to 252 bytes
[When master sends request message to slave]
Stores the requested processing.
[When slave sends response message to master]
Stores the result of processing execution.

Mitsubishi QJ71MT91 Specifications

General

Brand	Mitsubishi
Model	QJ71MT91
Category	Controller
Language	English