Chapter 3 Modbus Standard Function Details; Read Coils (Fc: 01H) - Mitsubishi Electric MELSEC iQ-R Series Reference Manual

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MODBUS STANDARD FUNCTION DETAILS
This chapter describes protocol data unit formats.
3.1

Read Coils (FC: 01H)

Operation description
Reads the status (ON/OFF) of one or multiple coils.
Request message format (from master to slave)
Function code
Start coil number specification
01H
(H)
Response message format (from slave to master)
■ When completed successfully
Function code
Number of read
bytes n
01H
• Device data 1 to n
b7
Device data 1
Device data n
• The read coil status is stored in the order of lower bit to higher bit.
• If the number of read points is not a multiple of eight, the remaining bits are all set to 0.
■ When completed with an error
Function code Data
Exception code
81H
3 MODBUS STANDARD FUNCTION DETAILS
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3.1 Read Coils (FC: 01H)
Data
(0000H to FFFFH)
(L)
Data
Device data 1
Number of read bytes n
b6 b5 b4 b3
Number of read points
(0001H to 07D0H)
(H) (L)
Device data n
b2 b1 b0
Bit device storage order
0: OFF
1: ON