Interpret protocol evidence
| No response | Transport, unit ID, timing, gateway route or device state. |
|---|---|
| Illegal function | Function unsupported by that unit/firmware. |
| Illegal data address | Wrong register range or zero/one-based mapping. |
| Illegal data value | Quantity/value or device-specific constraint. |
| Valid response, wrong value | Signedness, scaling, byte/word order or register map. |
RTU and TCP checks
For RTU verify framing, silent intervals and CRC. For TCP verify transaction/unit identifiers and gateway routing. Capture request/response pairs, retain exception frames and test documented read-only registers before writes.
Use legacy integration for gateway/replacement strategy, RS485 reverse engineering for proprietary buses, framing diagnosis and the pillar.
Provide transport/topology, captures, unit ID, requested function/register, expected engineering value and vendor map.