Read Holding Registers (Fc: 03) - Mitsubishi Electric QJ71MB91 User Manual

4
MODBUS STANDARD FUNCTIONS

4.6 Read Holding Registers (FC: 03)

Reads the values of one or more holding registers.
(1) Request message format (Master
Function code
(2) Response message format (Slave
(When completed normally)
Function code
(When completed with an error)
Figure 4.17 Read holding registers (Exception message)
Function Head holding register number
code (0000 to FFFF
H
(03 )
H
(H)
Figure 4.15 Read holding registers (Request message)
Function Number of
code read bytes
(03 ) n x 2 *1
H
Figure 4.16 Read holding registers (Normal response message)
Function code Data
Function
Exception
code 2
code *
(83 )
H
* 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
Slave)
Data
Read points
) (0001 to 007D
H H
(L)
(H)
Master)
Data
Device data . . .
1
(H) (L)
(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.
4.6 Read Holding Registers (FC: 03)
)
H
(L)
Device data
n
(H) (L)
4
1
2
3
4
5
6
7
8
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