Technical data

MODBUS Functions • 153
Description of the MODBUS Functions
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
6.3.6 Function Code FC6 (Write single register)
This function writes the value of one single output register to a slave device in
word format.
Request
The request specifies the reference number (register address) of the first output
word to be written. The value to be written is specified in the “Register
Value” field. The reference number of the request is zero based; therefore, the
first register starts at address 0.
Example: Write a value of 0x1234 to the second output register.
Byte Field name Example
Byte 0, 1 Transaction identifier 0x0000
Byte 2, 3 protocol identifier 0x0000
Byte 4, 5 length field 0x0006
Byte 6 Unit identifier 0x01 not used
Byte 7 MODBUS function code 0x06
Byte 8, 9 reference number 0x0001
Byte 10, 11 Register Value 0x1234
Response
The reply is an echo of the inquiry.
Byte Field name Example
.....
Byte 7 MODBUS function code 0x06
Byte 8, 9 Reference number 0x0001
Byte 10, 11 Register Value 0x1234
Exception
Byte Field name Example
.....
Byte 7 MODBUS function code 0x85
Byte 8 Exception code 0x01 or 0x02