Research Article
Detection and Blocking of Replay, False Command, and False Access Injection Commands in SCADA Systems with Modbus Protocol
Table 1
Various Modbus function codes and their actions on data.
| Function code | Action to be performed |
| 1 | Reading of coils | 2 | Reading of status registers | 3 | Reading holding registers | 4 | Reading of input registers | 5 | Writing to single coil | 6 | Writing to single holding register | 15 | Multiple coils: write | 16 | Multiple holding registers: write |
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