Function Code Fc16 (Write Multiple Registers); Function Code Fc23 (Read/Write Multiple Registers) - WAGO 750 Series Manual

108 • Fieldbus Communication
MODBUS Functions
4.2.3.10

Function Code FC16 (Write multiple registers)

This function writes a sequence of registers in a slave device in word format.
Request
The Request specifies the reference number (starting register), the word count
(number of registers to write), and the register data . The data is sent as 2 bytes
per register. The registers are zero-based; therefore, the first output is at
address 0.
Example: Set data in registers 0 and 1:
Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11
Byte 12
Byte 13, 14
Byte 15, 16
Response
Byte
.....
Byte 7
Byte 8, 9
Byte 10, 11
Exception
Byte
.....
Byte 7
Byte 8
4.2.3.11

Function Code FC23 (Read/Write multiple registers)

This function performs a combination of a read and write operation in a single
request. The function can write the new data to a group registers, and then
return the data of a different group.
Field name
Transaction identifier
protocol identifier
length field
Unit identifier
MODBUS function code
reference number
Word count
Byte Count
Register Value 1
Register Value 2
Field name
MODBUS function code
Reference number
Word Count
Field name
MODBUS function code
Exception code
Example
0x0000
0x0000
0x000B
0x01 not used
0x10
0x0000
0x0002
0x04
0x1234
0x2345
Example
0x10
0x0000
0x0002
Example
0x85
0x01 or 0x02
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