Aaron Graves, PhDude (Replica)

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crc16 modbus calculator

Posted on February 16, 2026 by Admin
Hex mode accepts bytes like 01 03 00 00 00 02, 0x01,0x03,0x00,0x00,0x00,0x02, or continuous hex 010300000002.
Enter payload data and click Calculate CRC16 Modbus.

What this CRC16 Modbus calculator does

This tool computes the CRC-16/Modbus checksum for a byte stream. It is commonly used in Modbus RTU communication to detect transmission errors on serial links (RS-485/RS-232).

The calculator uses the standard Modbus parameters:

  • Width: 16 bits
  • Polynomial: 0xA001 (reverse representation of 0x8005)
  • Initial value: usually 0xFFFF
  • Input reflected: yes
  • Output reflected: yes
  • XOR out: usually 0x0000
  • Byte order on wire: low byte first, then high byte

How to use it

1) Choose your input mode

Use Hex bytes for Modbus frame payloads (most common), or ASCII text if you want to hash a plain string.

2) Enter your data bytes

For a classic read-holding-registers request: 01 03 00 00 00 02.

3) Keep default initialization unless you need a variant

Standard Modbus uses FFFF for initial value and 0000 for final XOR.

4) Calculate and use the appended frame

The output includes both CRC bytes and the final message with CRC appended in the correct Modbus order.

CRC16 Modbus worked example

Input frame (without CRC): 01 03 00 00 00 02
Calculated CRC: 0x0BC4
Transmitted CRC bytes: C4 0B (low-high order)
Full RTU frame: 01 03 00 00 00 02 C4 0B

Common mistakes (and how to avoid them)

  • Byte order confusion: Modbus sends CRC low byte first.
  • Including the CRC in the CRC input: calculate over payload only.
  • Wrong polynomial or init value: many CRC-16 variants exist; Modbus is specific.
  • ASCII vs hex confusion: string "01" is bytes 30 31 in ASCII, not 01.

When to use a CRC16 Modbus calculator

This is useful during PLC commissioning, SCADA integration, serial gateway debugging, protocol learning, and verification of custom firmware implementations. If your slave device keeps rejecting frames, checking CRC quickly isolates whether the issue is checksum, framing, addressing, or function code.

Quick reference: Modbus RTU frame layout

  • Address (1 byte)
  • Function code (1 byte)
  • Data (N bytes)
  • CRC low (1 byte)
  • CRC high (1 byte)

Final thoughts

A reliable CRC calculator saves time and prevents subtle bugs. Keep this page handy as a practical Modbus checksum tool for protocol testing, diagnostics, and field troubleshooting.

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