An error response is returned if the query message received from the master has an illegal function, address, or data. No response is returned for a parity, CRC, overrun, framing, or busy error.
Note: No response message is sent in the case of broadcast communication.
| Subordinate Address | Function | Exception Code | CRC Check | |
|---|---|---|---|---|
| (8 bit) | H80 + function (8 bit) | (8 bit) | L (8 bit) | H (8 bit) |
| Message | Setting Description |
|---|---|
| Subordinate Address | Address received from the master. |
| Function | Master-requested function code + H80 |
| Exception Code | See Table 3. |
| Code | Error Item | Error Description |
|---|---|---|
| 01 | Illegal Function | The set function code in the query message from the master cannot be processed by the subordinate. |
| 02 | Illegal Data Address1 | The set register address in the query message from the master cannot be processed by the subordinate. |
| 03 | Illegal Data Value | The set data in the query message from the master cannot be processed by the subordinate. |
Note: An error occurs if all accessed holding registers do not exist.
Note: Data read from a nonexistent holding register is 0, and data written there
is invalid.
1 An error does not occur in the following
cases:
- a. Function code H03 (Read holding register data) - when the number of points is 1 or more and there is one or more holding registers from which the data may be read.
- b. Function code H10 (write multiple holding register data) - when the number of points is 1 or more and there is one or more holding registers to which the data may be written. When the function code H03 or H10 is used to access multiple holding registers, an error does not occur if a nonexistent holding register, read-disabled register, or write-disabled register is accessed.