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Modbus Frame Builder
Build RTU & TCP frames, auto-calculate CRC16, validate messages — all offline.
Frame Parameters
RTU: 1–247 · TCP: 0–255 (device-specific)
Select the Modbus function code for your frame
0x0000–0xFFFF
Max 125 registers
Coil: ON/OFF, 1/0, 0xFF00/0x0000 · Register: 0–65535
Live Frame Output
:01 03 00 00 00 01 ?? ??
01 03 00 00 00 01
SLV01
FC03
ADDR00 00
QTY00 01
XXXX
TID00 01
PID00 00
Len00 06
UID01
CRC16 Validator
Paste a received Modbus RTU frame to verify its CRC integrity.
Spaces optional. Leading colon (:) stripped automatically.
CRC16 Reference — Standard Modbus Polynomial
Polynomial
0x8005 (CRC-16/MODBUS)
Initial Value
0xFFFF
Reflection
Reflected (LSB first)
Output XOR
0x0000
Industrial context: Modbus RTU appends CRC16 to every frame for error detection on RS-485 serial networks. Modbus TCP replaces CRC with a 7-byte MBAP (Modbus Application Protocol) header. PLCs, RTUs, and gateways use these frame formats for SCADA and IIoT communication.
Next step
Validate the result against device documentation and known examples. Find commissioning checklists and technical guides in the resource library.
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