Technical data

Fieldbus Communication • 223
MODBUS Functions
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
4.3.3.6 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 out-
put 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