AD7380 datasheet(24/31 Pages) AD

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AD7381-4

Data Sheet

Rev. 0 | Page 24 of 31

CRC Polynomial

For CRC checksum calculations, the following polynomial is

always used: x8 + x2 + x + 1.

To generate the checksum, the 14-bit data conversion result of

the four channels are combined to produce a 56-bit data

stream. The 8 MSBs of the 56-bit data are inverted and then the

data is appended by eight bits to create a number ending in

eight Logic 0s. The polynomial is aligned such that its MSB is

adjacent to the leftmost Logic 1 of the data. An exclusive OR

(XOR) function is applied to the data to produce a new, shorter

number. The polynomial is again aligned such that its MSB is

adjacent to the leftmost Logic 1 of the new result, and the

procedure is repeated. This process repeats until the original

data is reduced to a value less than the polynomial, which is the

8-bit checksum.

For example, the AD7381-4 polynomial is 100000111. Let the

original data of four channels be 0xAAAA, 0x5555, 0xAAAA,

and 0x5555. The eight MSBs of the data are inverted. The data

is then appended to include eight 0s on right. In the final XOR

operation, the reduced data is less than the polynomial.

Therefore, the remainder is the CRC for the assumed data.

Table 14. Example CRC Calculation for 4-Channel, 16-Bit Data

Data

1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 X1 X1 X1 X1 X1 X1 X1 X1

Process Data 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0

0 0 0 0 0 0 0

1 0 0 0 0 0 1 1 1

1 0 1 0 0 0 1 1 0

1 0 0 0 0 0 1 1 1

1 0 0 0 0 0 1 1 0

1 0 0 0 0 0 1 1 1

1 1 0 0 1 0 1 0 1

1 0 0 0 0 0 1 1 1

1 0 0 1 0 0 1 0 0

1 0 0 0 0 0 1 1 1

1 0 0 0 1 1 1 0 1

1 0 0 0 0 0 1 1 1

1 1 0 1 0 0 1 0 1

1 0 0 0 0 0 1 1 1

1 0 1 0 0 0 1 0 0

1 0 0 0 0 0 1 1 1

1 0 0 0 0 1 1 1 0

1 0 0 0 0 0 1 1 1

1 0 0 1

1 0 0 0

CRC

X means don’t care.

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