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AD7779 CRC calculation

Question asked by dmitryneuro on Jul 6, 2016
Latest reply on Jul 6, 2016 by musach

1. XOR operation in CRC calculation example in AD7779 datasheet Rev. 0 http://www.analog.com/media/en/technical-documentation/data-sheets/AD7779.pdf

Table 42. Example CRC Calculation for 12-Bit Data.png

"The 8-bit CRC polynomial used is x 8 + x 2 + x + 1."

"To generate the checksum, the data is left shifted by eight bits to create a number ending in eight Logic 1s."

"56 bits = chip error + 3 ADC channel bits (010) + 24 data bits (Channel 2) + chip error + 3 ADC channel bits (011) + 24 data bits (Channel 3)"

 

2. Example from article by Ken Kavanagh an applications engineer in ADI's Precision DAC Group http://www.analog.com/library/analogDialogue/archives/45-02/CRC.html

AD45-02_BB_FIG_02.jpg

"The CRC-8 algorithm uses the polynomial C(x) = x8 + x2 + x1 + 1. For x = 2, this is equivalent to the binary value 100000111. To generate the checksum, the 24-bit data is left-shifted by eight bits to create a 32-bit number ending in eight Logic 0s."

 

So for calculation of CRC based on CRC Polynom 10000011 there will be 64 bits = 56bits + 8 bits of Logic 1s?

In AD7779 datasheet nothing said about 64 bits for CRC calculation, but said "56 bits are used to calculate the 8-bit CRC."

 

Or CRC Polynom will be 100000111 as in Ken Kavanagh example?

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