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 | Reg | Count | Count | CRC | CRC | ||
|
|
| HI | LO | HI | LO | HI | LO | ||
01 | 03 | 00 | 03 | 00 | 01 | 74 | 0A | |||
|
|
| Response from Transmitter |
|
|
| ||||
| Address | Cmd | Byte | Byte |
| Data | Data | CRC | CRC |
|
|
|
| Count | Count |
| HI | LO | HI | Lo |
|
|
|
| HI | 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 | Reg | Data | Data | CRC |
| CRC |
| |
|
|
| HI | LO | HI | LO | HI |
| LO |
| |
| 01 | 06 | 00 | 01 | 00 | C8 | D9 |
| 9C |
| |
|
| Response from Transmitter |
|
|
|
| |||||
| Address | Cmd | Reg | Reg | Data | Data |
| CRC | CRC |
| |
|
|
| HI | LO | HI | LO |
| HI | 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.
Page 11 of 23
11/14/2006 | Rev. 14 |
