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Page 11 of 23
11/14/2006 Rev. 14
The following is an example of a function 03 call for data at memory location 03. The
value returned by the instrument is the hex value 1E.
Transmit from Host or Master
Address Cmd Reg
HI
Reg
LO
Count
HI
Count
LO
CRC
HI
CRC
LO
01 03 00 03 00 01 74 0A
Response from Transmitter
Address Cmd Byte
Count
HI
Byte
Count
LO
Data
HI
Data
LO
CRC
HI
CRC
Lo
01 03 00 02 00 1E 38 4C
Note that all the values are interpreted as hexadecimal values. The CRC calculation is
based on the A001 polynomial for RTU Modbus. The function 04 command structure is
similar to the 03 structure.
The following is an example of a function 06 call to change data in register 01 to 200. The
response from the instrument confirms the new value as being set.
Transmit from Host or Master
Address Cmd Reg
HI
Reg
LO
Data
HI
Data
LO
CRC
HI
CRC
LO
01 06 00 01 00 C8 D9 9C
Response from Transmitter
Address Cmd Reg
HI
Reg
LO
Data
HI
Data
LO
CRC
HI
CRC
LO
01 06 00 01 00 C8 D9 9C
The Transmitter will respond to several error conditions. The three exception codes that
will generate a response from the instrument are:
01 – Illegal Function
02 - Illegal Data Address
03 – Illegal Data Value
04 – Slave Device Failure
The response from the Transmitter with an exception code will have the most significant
bit of the requested function set followed by the exception code and the high and low CRC
bytes.