Read Coils (Fc: 01) - Mitsubishi Electric QJ71MB91 User Manual

4
MODBUS STANDARD FUNCTIONS

4.4 Read Coils (FC: 01)

Reads the status (ON/OFF) of one or more coils.
(1) Request message format (Master
(2) Response message format (Slave
(When completed normally)
(When completed with an error)
Function code
Figure 4.11 Read coils (Exception message)
Function code
Function Head coil number
(0000 to FFFF
code
H
(01 )
H
(H)
Figure 4.9 Read coils (Request message)
Function code
Function Number of Device data
code read bytes
(01 ) n
H
(Device data 1 to n)
Device data 1
Device data n
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.
Figure 4.10 Read coils (Normal response message)
Data
Function code Exception
(81 ) code* 1
H
* 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
Slave)
Data
Read points
) (0001 to 07D0
H H
(L)
(H)
Master)
Data
Device data
1
(Number of read bytes n)
b7 b6 b5 b4 b3
4.4 Read Coils (FC: 01)
)
H
(L)
n
b2 b1 b0
Bit device
storage order
0 : OFF
1 : ON
4
1
2
3
4
5
6
7
8
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