Mitsubishi QJ71MB91, User Manual

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4
MODBUS(R) STANDARD FUNCTIONS
4.6 Read Holding Registers (FC: 03)
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4.6 Read Holding Registers (FC: 03)
Reads the values of one or more holding registers.
(1) Request message format (Master Slave)
(2) Response message format (Slave Master)
(When completed normally)
(When completed with an error)
* 2 Exception and error codes are stored in the buffer memory in the case of error completion.
Refer to the following for storage location, confirmation methods, and detailed contents.
Section 11.4
Figure 4.15 Read holding registers (Request message)
Figure 4.16 Read holding registers (Normal response message)
Figure 4.17 Read holding registers (Exception message)
Data
(L) (L)
Function code
Function
code
(03
H
)
Head holding register number
(0000
H
to FFFF
H
)
Read points
(0001
H
to 007D
H
)
(H)
(H)
Data
. . .
(L) (L)
Function code
Function
code
(03
H
)
Number of
read bytes
n x 2 *1
Device data
1
Device data
n
(Number of read bytes n x 2)
*1 For example, if n = 4, the number of read
bytes is calculated as 4 x 2 = 8 bytes.
(H) (H)
Data Function code
Function
code
(83
H
)
Exception
code *
2