Mitsubishi QJ71MB91, User Manual

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4
MODBUS(R) STANDARD FUNCTIONS
4.4 Read Coils (FC: 01)
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4.4 Read Coils (FC: 01)
Reads the status (ON/OFF) of one or more coils.
(1) Request message format (Master Slave)
(2) Response message format (Slave Master)
(When completed normally)
(When completed with an error)
* 1 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 4.9 Read coils (Request message)
Figure 4.10 Read coils (Normal response message)
Figure 4.11 Read coils (Exception message)
Data
(L) (L)
Function code
Function
code
(01
H
)
Head coil number
(0000
H
to FFFF
H
)
Read points
(0001
H
to 07D0
H
)
(H) (H)
Data
b0 b1 b2 b3 b4 b5 b6 b7
Function code
Function
code
(01
H
)
Number of
read bytes
n
Device data
1
Device data
n
(Number of read bytes n)
(Device data 1 to n)
Device data 1
Device data n
Bit device
storage order
0 : OFF
1 : ON
The read coil statuses are stored in order from low-order to high-order bits.
When the number of read points is not a multiple of 8, the excess bits turn to 0.
Data
Function code
(81
H
)
Function code
Exception
code*
1