BQ76925 CRC check

Hi Arking,

When using the CRC every transaction will contain 3 bytes: (Address,R/W),(Data),(CRC). The CRC is calculated over the first 2 bytes in the transaction: (Address,R/W),(Data). For example, suppose you want to write the data 0x55 to register address 0x02. The 7-bit combined address is calculated as shown in Table 4 in the datasheet and is equal to 0x22 (010_0010). The R/W bit is '0' for a write and is added on the right-hand side of the combined address so that the transmitted address byte = 0x44 (0100_0100). The CRC is then calculated over 0x44,0x55 and is equal to 0xA3.

There are a number of techniques for computing the CRC. Here is some pseudo-code that shows one way of doing it:

char poly = 0x07          # 8-bit polynomial
char crc = 0x00           # Initialize 8-bit CRC
for each byte in message: # Loop over all bytes in the message
    crc = crc xor byte
    for index = 1 to 8:   # Loop over all bits in the CRC
        if crc > 127:     # If msb is set, shift left and XOR with poly
            crc = crc << 1
            crc = crc xor poly
        else:             # Else just shift left
            crc = crc << 1

Best Regards