CRC Generating and Checking - Microchip Technology

2000 Microchip Technology 1AN730 INTRODUCTIONThis application note describes the Cyclic RedundancyCheck (CRC) theory and implementation. The CRCcheck is used to detect errors in a message. Two imple-mentations are shown: Table driven CRC calculation Loop driven CRC calculationThis application describes the implementation of theCRC-16 polynomial. However, there are several for-mats for the implementation of CRC such asCRC-CCITT, CRC-32 or other is a common method for detecting errors in trans-mitted messages or stored data. The CRC is a verypowerful, but easily implemented technique to obtaindata reliability. THEORY OF OPERATIONThe theory of a CRC calculation is straight forward. Thedata is treated by the CRC algorithm as a binary num-ber. This number is divided by another binary numbercalled the polynomial. The rest of the division is theCRC checksum, which is appended to the transmittedmessage. The receiver divides the message (includingthe calculated CRC), by the same polynomial the trans-mitter used.

AN730 DS00730A-page 4 Preliminary 2000 Microchip Technology Inc. LOOP DRIVEN CRC IMPLEMENTATION This section describes the loop driven CRC implemen-tation. This implementation is derived from the hard-

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