Mitsubishi Electric MELSEC iQ-F FX5 User Manual page 70

Read holding registers
Reads the values of one or more holding registers.
Supports the MODBUS serial communication and MODBUS/TCP communication.
■Request message format (Master  Slave)
■Response message format (Slave  Master)
(When completed normally)
Function code
*1 For example, if n = 4, the number of bytes is calculated as 4  2 = 8 bytes.
(When completed with an error)
*2 Exception and error codes are stored in special registers in the case of error completion. Refer to the following sections for the storage
location, confirmation methods, and other detailed contents.
MODBUS serial communication: Page 35 Related Devices
MODBUS/TCP communication : Page 58 Related Devices
APPX
68
Appendix 3 The frame specifications
Function code
Function
code register number
(03H) (0000H to FFFFH)
Function Number of read
code bytes
m = n  2 *1
(03H)
Data
Head holding
(H) (L)
Data
. . .
Device data
1
(H) (L)
(Number of read bytes n  2)
Data
Function code
Function Exception
code
code *2
(83H)
Read points
(0001H to 007DH)
(H) (L)
Device data
n
(H) (L)