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Example CRC Calculation. As was previously shown, flipping the same bits in each byte of a message produces a checksum identical to that of the original message The following example demonstrates that a CRC calculation of those same messages produce a vastly different result - PowerPoint PPT Presentation
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Example CRC Calculation As was previously shown, flipping the same bits in each byte of a
message produces a checksum identical to that of the original message
The following example demonstrates that a CRC calculation of those same messages produce a vastly different result
Original Message bits = ‘Hi’ = 4869h = 0100 1000 0110 1001 Swapped Message bits = ‘jK’ = 6A4Bh = 0110 1010 0100 1011
*Note: An 8-bit CRC is used in this example for ease of calculation, however 16 and 32-bit CRCs are more useful
*Note 2: The XOR gate is located after bit 4 for this example, but this is not always the case.
8-bit CRC hardware diagram
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1 Note the effect of the XOR gate on bits 0 and 5
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
000 00010 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
011 00010 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
000 00010 0
000 00101 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
011 00010 0
110 00101 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
000 00010 0
000 00101 1
000 01010 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
011 00010 0
110 00101 1
101 01011 0
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
000 00010 0
000 00101 1
000 01010 0
000 10100 0
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
011 00010 0
110 00101 1
101 01011 0
011 10110 1
8-BIT CRC for ‘Hi’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00010 0
000 00100 0
000 01001 1
000 10010 0
001 00100 0
010 01000 0
100 10000 0
000 00000 1
000 00001 1
000 00010 0
000 00101 1
000 01010 0
000 10100 0
001 01001 1
8-BIT CRC for ‘jK’ INPUT
000 00000 Init.
000 00000 0
000 00001 1
000 00011 1
000 00110 0
000 01101 1
000 11010 0
001 10101 1
011 01010 0
110 10100 0
100 01000 1
001 10001 0
011 00010 0
110 00101 1
101 01011 0
011 10110 1
111 01101 1
CRC for ‘Hi’ = 00101001 = 29hCRC for ‘jK’ = 11101101 = EDh
Results:
