AD7617 datasheet(41/52 Pages) AD

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AD7617

Data Sheet

Rev. 0 | Page 40 of 51

If the CRC function is enabled, a CRC is calculated on the

conversion results for Channel VxA and Channel VxB. The CRC is

calculated and transferred on the serial or parallel interface after

the conversion results are transmitted, depending on the

configuration of the device. The Hamming distance varies relative

to the number of bits in the conversion result. For conversions with

≤119 bits, the Hamming distance is 4. For >119 bits, the Hamming

distance is 1, that is, 1-bit errors are always detected.

The CRC polynomial in use on the AD7617 is

x8 + x2 + x + 1

The following is a pseudocode description of how the CRC is

implemented in the AD7617:

crc = 8’b0;

i = 0;

x = number of conversion channel pairs;

for (i=0, i<x, i++) begin

crc1 = crc_out(An,Crc);

crc = crc_out(Bn,Crc1);

i = i +1;

end

where the function crc_out(data, crc) is

crc_out[0] = data[14] ^ data[12] ^ data[8] ^

data[7] ^ data[6] ^ data[0] ^ crc[0] ^

crc[4] ^ crc[6];

crc_out[1] = data[15] ^ data[14] ^ data[13]

^ data[12] ^ data[9] ^ data[6] ^ data[1] ^

data[0] ^ crc[1] ^ crc[4] ^ crc[5] ^ crc[6]

^ crc[7];

crc_out[2] = data[15] ^ data[13] ^ data[12]

^ data[10] ^ data[8] ^ data[6] ^ data[2] ^

data[1] ^ data[0] ^ crc[0] ^ crc[2] ^ crc[4]

^ crc[5] ^ crc[7];

crc_out[3] = data[14] ^ data[13] ^ data[11]

^ data[9] ^ data[7] ^ data[3] ^ data[2] ^

data[1] ^ crc[1] ^ crc[3] ^ crc[5] ^ crc[6];

crc_out[4] = data[15] ^ data[14] ^ data[12]

^ data[10] ^ data[8] ^ data[4] ^ data[3] ^

data[2] ^ crc[0] ^ crc[2] ^ crc[4] ^ crc[6]

^ crc[7];

crc_out[5] = data[15] ^ data[13] ^ data[11]

^ data[9] ^ data[5] ^ data[4] ^ data[3] ^

crc[1] ^ crc[3] ^ crc[5] ^ crc[7];

crc_out[6] = data[14] ^ data[12] ^ data[10]

^ data[6] ^ data[5] ^ data[4] ^ crc[2] ^

crc[4] ^ crc[6];

crc_out[7] = data[15] ^ data[13] ^ data[11]

^ data[7] ^ data[6] ^ data[5] ^ crc[3] ^

crc[5] ^ crc[7];

The initial CRC word used by the AD7617 is an 8-bit word

equal to zero. The XOR operation described in the preceding

code is executed to calculate each bit of the CRC word for the

conversion result, AN. This CRC word (crc1) is then used as the

starting point for calculating the CRC word (crc) for the

conversion result, BN. The process repeats cyclically for each

channel pair converted.

Depending on the mode of operation of the AD7617, the status

via an extra read command over the serial or parallel interface.

The user can then repeat the XOR calculation described in the

preceding code for the received conversion results to check

whether both CRC words match. See Figure 69 for a description

of how the CRC word is appended to the data for each mode of

operation.

Figure 69. CRC Readback for All Modes

CONVST

BUSY

CRCAB(x)

DATA

CRCAB(x:z)

DATA

CRCAB(x)

SDOA

CRCAB(x)

SDOB

CRCAB(x:z)

SDOA

CRCAB(x:z)

SDOB

PARALLEL/SERIAL (1-WIRE),

SEQUENCER/MANUAL MODE

PARALLEL/SERIAL (1-WIRE),

BURST

SERIAL (2-WIRE),

SEQUENCER/MANUAL MODE

SERIAL (2-WIRE),

BURST

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