Technical data

156 • MODBUS Functions
Description of the MODBUS Functions
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
6.3.9 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 Field name Example
Byte 0, 1 Transaction identifier 0x0000
Byte 2, 3 protocol identifier 0x0000
Byte 4, 5 length field 0x000B
Byte 6 Unit identifier 0x01 not used
Byte 7 MODBUS function code 0x10
Byte 8, 9 reference number 0x0000
Byte 10, 11 Word count 0x0002
Byte 12 Byte Count 0x04
Byte 13, 14 Register Value 1 0x1234
Byte 15, 16 Register Value 2 0x2345
Response
Byte Field name Example
.....
Byte 7 MODBUS function code 0x10
Byte 8, 9 Reference number 0x0000
Byte 10, 11 Register Value 0x0002
Exception
Byte Field name Example
.....
Byte 7 MODBUS function code 0x85
Byte 8 Exception code 0x01 or 0x02