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APPENDIX A CRC-16 Calculation
CRC-16 Generation
Modbus RTU Protocol uses the Reverse CRC Generation algorithm.
CRC Generation procedure
Refer to “Appendix B” for detail s on the C code.
1. Load a 16-bit register with FFFF hex(all 1 ’ s). Call this the CRC register.
2. Exclusive OR the first 8-bit byte of the message with the low-order byte of the 16-bit CRC
register, putting the result in the CRC register.
3. Shift the CRC register one bit to the right (toward the LSB), zero-filling the MSB. Extract
and examine the LSB.
4. (If the LSB was 0 ): Repeat Step 3(another shift)
5. (If the LSB was 1): Exclusive OR the CRC register with the polynomial value A))1 hex (1010
0000 0000 0001)
6. Repeat Steps 3 and 4 until 8 shifts have been performed. When this is done, a complete
8-bit byte will have been processed.