AD4134 CRC FAQ

CRC or cyclic redundancy check is a checksum algorithm to detect errors in data transmission.

A checksum is appended to the data to help the receiver detect errors.

AD4134/AD7134 uses CRC-6 with polynomial x^6 + x^5 + x^2 + x + 1 and default seed value of 0x25

Below are the steps in calculating the checksum

Generating CRC checksum

1. Initialize the output code by performing bitwise XOR on the first 6 bits with the seed value, in our case 0x25
2. Append 6 zero bits for CRC-6
3. Compute the CRC checksum by
   1. Polynomial Division
   2. Bitwise XOR

Verifying the CRC checksum

1. Initialize the output code by performing bitwise XOR on the first 6 bits with the seed value: 0x25
2. Divide the received data by the known polynomial - 1100111
3. The remainder should be 0 for valid data

Example:

Generating CRC checksum

1. Initialize the output code by performing bitwise XOR on the first 6 bits with the seed value, in our case 0x25

24 bits data + 2 bits header:

0011 0000 0000 1000 0110 1011 11

Default seed value: 0x25 = 100101

First 6 bits: 001100

XOR this first 6 bits with the seed à 100101 ^ 001100 = 101001 <-- Use this as first 6-bits of message data

2.Append 6 zero bits for CRC-6

Initialized message data: 10100100000010000110101111000000

3. Compute the CRC checksum by

1. 1. Polynomial Division
   2. Bitwise XOR

Initialized message data: 10100100000010000110101111000000

Polynomial (P(x)): 1100111

Compute the CRC

Remainder = 01011 = 0x13

Transmitted data:

24 bits data + 2 bits header + 6 bit CRC

0011 0000 0000 1000 0110 1011 + 11 + 01 0011

Verifying the CRC checksum

1. Initialize the output code by performing bitwise XOR on the first 6 bits with the seed value:  0x25

Initialized message data: 10100100000010000110101111010011

2. Divide the received data by the known polynomial - 1100111

Initialized message data: 10100100000010000110101111010011

Polynomial (P(x)): 1100111

Remainder = 0

3. The remainder should be 0

Data received is correct!