| Function code | Name | Description |
|---|---|---|
| 81 | Read coil status exception code | Unsuccessful read of discrete outputs status |
| 82 | Read digital input status exception code | Unsuccessful read of discrete inputs status |
| 83 | Read holding registers exception code | Unsuccessful read of the contents of output registers contents |
| 84 | Read input registers exception code | Unsuccessful read of the contents of input registers contents |