Modbus RTU CRC-16 Calculator

Professional debugging & frame verification tool for OT engineers.

Checksum (CRC-16)
00 00
(Low Byte First / Little-Endian)
Full Frame with CRC
— —

Frame Structure Analysis:

Enter a valid hex string to see breakdown…
Understanding Modbus RTU CRC-16 Calculation +

RS485 serial communications are frequently disrupted by electrical noise from VFDs and heavy machinery in harsh industrial environments. Cyclic Redundancy Check (CRC-16) is an important error-detecting code that is added at the end of each Modbus RTU frame. It ensures the payload (Slave Address, Function Code and Data) reaches the SCADA system or PLC in exactly the same format as it was sent without any bit-flip corruption.

The 0xA001 Polynomial & Byte Order (LSB First)

Modbus protocol CRC is 0xA001 polynomial (0xFFFF as initial value) unlike standard CRC implementations. More importantly, Modbus RTU specifically requires that the checksum be sent in Little-Endian (LSB First) format. This means that the Low Byte is sent first, then the High Byte. Our calculator handles this byte swapping for you automatically. Your hex dumps will be ready to inject into terminal software directly.

Hardware Diagnostics & Root-Cause Fix

Stop Software Polling Jitter & RS485 Packet Loss

When your CRC is mathematically correct but your field bus keeps timing out, your software is blindly fighting hardware latency. Upgrade to the Valtoris SS100 Gateway with native sub-3ms automated hardware polling and galvanic isolation.

💡 Not ready for hardware upgrades yet? We also provide a free, standalone desktop utility to diagnose live serial bus frames: Download Windows Diagnostic Tool (.RAR) ↗

Engineering debugging tools developed for OT professionals by Valtoris.
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