Table of Contents
Advertisement
4
MODBUS STANDARD FUNCTIONS
4.3.12 Read/Write multiple registers (FC: 23)
4 - 20
Reads and writes data from and to multiple holding registers.
Write is executed first and read is then executed.
(1) Request message format (Master → Slave)
1: The number of points specified as the write points must be matched with the
number of bytes.
(2) Response message format (Slave → Master)
(When completed normally)
Function code
Number of bytes
Function code
n 2
(17
)
H
(When completed with an error)
Function code
Function code
Exception
code *2
(97
)
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
Read device data
1
(H)
(L)
Data
MELSEC-Q
Read: 1 to 125 points
Write: 1 to 121 points
Data
Read device data
(H)
(Number of bytes n 2)
n
(L)
4 - 20
Advertisement
Table of Contents
