Read Input Registers (Fc: 04) - Mitsubishi QJ71MT91 User Manual

4 MODBUS STANDARD FUNCTIONS
R

4.3.4 Read input registers (FC: 04)

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Reads the values of one or more input registers.
(1) Request message format (Master
Function code
Head input register number
Function code
(04 ) (0000
H
(H)
(2) Response message format (Slave
(When completed normally)
Function code
Function code Number of
read bytes
(04 )
H
n 2*1
(When completed with an error)
Function code
Function code
Exception
(84 )
H
2: When completed with an error, the exception code and error code are stored
into the buffer memory.
Refer to Section 11.3 for the storage location, confirmation method and more
details.
Number of accessible devices with one message
Data
to FFFF ) (0001
H H
(L) (H)
Device data
1
(H)
Data
code*
1 to 125 points
Slave)
Read points
to 007D )
H H
(L)
Master)
Data
(L)
(Number of read bytes n 2)
*1:
For example, when n = 4, the number of
read bytes is 4
MELSEC-Q
Device data
n
(H) (L)
2 = 8 bytes.
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