ROOTCASTLE / LABORATIO INGENIORUM
Inspector protocolus
Decode Modbus RTU, UART et CAN frames.
LOCAL CALCULATION · NO DEVICE CONNECTION
Modbus RTU decoder
✓ Valid frame · Request
| Field | Bytes | Value |
|---|---|---|
| slave | 01 | 1 |
| function | 03 | 3 Read Holding Registers |
| start | 00 00 | 0 (0x0000) |
| quantity | 00 0A | 10 |
| crc | C5 CD | 0xCDC5 = 0xCDC5 |
Model and assumptions
RTU frame: address, function, data, CRC-16 (reflected polynomial 0xA001, initial 0xFFFF, low byte first). The same function code has different lengths in request and response; automatic direction can be wrong for ambiguous frames. Addresses are zero-based; the 40001 notation is a device convention. Word order of 32-bit values depends on the device.
CRC: c=0xFFFF; c^=byte; 8×{ c = c&1 ? (c>>1)^0xA001 : c>>1 }
Quid est
Faultus de communicatione in campo quod plurima sunt: wrong CRC, wrong address, mixed-up word order et timeouts. Frames copiatas ab analysatore aut log serialem inserere ut quis quisque falsum sit, code exception device et interpretationes probabiles registri valorum.
Limites
Instrumentum non connectet ad device aut mittat data; omnia calculatio in tuo browser currit. Modbus ASCII, Modbus TCP, CAN FD et J1939/CANopen interpretatio payloadis in scope non sunt. Directio automatica pro frame ambiguis potest esse errata; scele manualiter.
Referentia
Modbus over Serial Line V1.02 · Modbus Application Protocol V1.1b3 · ISO 11898-1:2015 (CAN data link layer) · Catalogus CRC
Modelus educationalis. Resulta non sunt sufficientia ad diagnosim machinam aut definire fines operandi saluti.