DAC8741H: CRC

Ryan Stephen

Part Number: DAC8741H

Trying to figure out the CRC for the DAC8741H. I know the polynomial is polynomial x8 + x2 + x + 1. Which i have interpret as a mask 0x87 is this correct?

What data bytes are included in the calculation? Is it just the data word or does it include the address + RW bit? Can somebody give an example of the CRC value for what i should expect to see for a packet that looks like:

0x820000

(Read command of the Control register to check CRC_EN bit is set)

Thanks

over 2 years ago

0 Paul_Frost over 2 years ago

TI__Guru 53193 points

Hi Ryan,

The mask would actually be 0x107. Here is a snippet of code you can use to help calculate the CRC.

unsigned int calculateCRC(unsigned int addr, unsigned int regdata){
    unsigned int data[] = {addr,  ( (regdata & 0xff00) >> 8 ), regdata & 0xff};
    static unsigned int len = 3;
    unsigned int crc = 0x00;
    size_t i, j;
    for (i = 0; i < len; i++) {
        crc ^= data[i];
        for (j = 0; j < 8; j++) {
            if ((crc & 0x80) != 0)
                crc = (unsigned int)((crc << 1) ^ 0x107);
            else
                crc <<= 1;
        }
    }
    return crc & 0xff;

My calculator shows that you would append 0xDD to your value.

0x820000DD.

Thanks,

Paul

0 Ryan Stephen over 2 years ago in reply to Paul_Frost

Prodigy 30 points

Hi Paul

Thanks, would you mind explaining why the mask is 16bit? I am quite confused as the largest order for the polynomial is 8.

Thanks

0 Paul_Frost over 2 years ago in reply to Ryan Stephen

TI__Guru 53193 points

Consider that the largest order is x^8, which could be written as 256. The value 256 can only be represented with a 9 bit number. so the polynomial is 'b 1 0000 0111.

0 Ryan Stephen over 2 years ago in reply to Paul_Frost

Prodigy 30 points

Perfect, makes sense. Thank you very much this has solved it.

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DAC8741H: CRC