[FAQ] TPS2HCS10-Q1: CRC Calculation Function Example

Part Number: TPS2HCS10-Q1

Tool/software:

The TPS2HCS10-Q1 and other TI Smart eFuse High-Side Switch devices has an optional cyclic redundancy check (CRC) feature to ensure each SPI frame (SPI Format: COPL = 0, CPHA = 1) is transmitted and received properly. This CRC calculation is based on the CRC-4-ITU standard, with a polynomial of x⁴ + x + 1 and a starting value of 1111. For more information, see the TPS2HCS10-Q1 data sheet. Please see below a code example on how to calculate the CRC bits:

To calculate CRC on the data sent by the SPI controller (MCU or processor) to the Smart eFuse High-Side Switch, the below algorithm is used.

To calculate CRC on the data sent by the Smart eFuse High-Side Switch to the SPI controller, the below algorithm is used with another step at the end. One of the following must happen after the below algorithm is run:

-Perform the same CRC calculation using the CRC algorithm result on an additional "1111" (the first four bits of the CRC byte sent from the SDO pin).

OR

-XOR the CRC algorithm result by 0x02.

uint8_t crc_encode(uint8_t send_rec_bytes[3])
{
  uint8_t crc_start = 0x0F;
  uint8_t crc_polynomial = 0x03;
  uint8_t crc_result = crc_start;
  uint8_t bitnum = 0;
  uint8_t bytenum = 0; 

for(bytenum = 0; bytenum < 3; bytenum++)
  {
    for(bitnum = 0; bitnum < 8; bitnum++)
    {
      if((((send_rec_bytes[bytenum] >> (7-bitnum)) & 0x01) ^ ((crc_result & 0x08) >> 3)) > 0)
        crc_result = crc_polynomial ^ ((crc_result << 1) & 0x0F);

      else
        crc_result = (crc_result << 1) & 0x0F;
    }

  }

  for(bitnum = 0; bitnum < 4; bitnum++)
  {
    if(((crc_result & 0x08) >> 3) > 0)
      crc_result = crc_polynomial ^ ((crc_result << 1) & 0x0F);
    else
      crc_result = (crc_result << 1) & 0x0F;
  }
  return crc_result;
}