DAC8760: CRC-8-ATM Calculation algorithm

Hi,

I'm pretty much doing just as the links you provided, except I'm not using a table yet. I wanted to verify that I can communicate with the DAC using the CRC before creating the table.

Here's the code:

BYTE CalcCRC8(int count, BYTE *pdata)
{
  int bit, i = 0;
  BYTE crc = 0x00;

  while(i < count) // for each byte
  {
    crc ^= *pdata; // Get the data byte
    for(bit = 0; bit < 8; bit++)
    {
      if((crc & 0x80) != 0x00)
        crc = (crc << 1) ^ CRC8_ATM;  // CRC8_ATM = 0x07
      else
        crc <<= 1;
    } // end for
    pdata++; // next byte
    i++;
  } // end while

  return crc;
} /* End CalcCRC8 */

and below is the calling function:

void DAC8760_Out_crc(const int ch, const uint value)
{
  W2B val;
  uint junk;
  int time;
  BYTE msg[3];
  BYTE crc;

  val.w = value;

  // Address byte = DAC REG
  msg[0] = DAC8760_DAC_REG;
  msg[1] = val.b[1]; // MSB
  msg[2] = val.b[0]; // LSB
  crc = CalcCRC8(3, msg);

  // Address byte
  DAC_SPI_OUT_BUF = DAC8760_DAC_REG;
  time = DAC_SPI_WAIT_TM;
  WAIT4_SPI2_XMIT;
  while((!DAC_SPI_RBF) && (time-- > 0)); // wait till finished
  junk = DAC_SPI_IN_BUF;
  DAC_SPI_OUT_BUF = val.b[1]; // MSB
  time = DAC_SPI_WAIT_TM;
  WAIT4_SPI2_XMIT;
  while((!DAC_SPI_RBF) && (time-- > 0)); // wait till finished
  junk = DAC_SPI_IN_BUF;
  DAC_SPI_OUT_BUF = val.b[0]; // LSB
  time = DAC_SPI_WAIT_TM;
  WAIT4_SPI2_XMIT;
  while((!DAC_SPI_RBF) && (time-- > 0)); // wait till finished
  junk = DAC_SPI_IN_BUF;
  DAC_SPI_OUT_BUF = crc; // the CRC
  time = DAC_SPI_WAIT_TM;
  WAIT4_SPI2_XMIT;
  while((!DAC_SPI_RBF) && (time-- > 0)); // wait till finished
  junk = DAC_SPI_IN_BUF;

  ENTER_CRITICAL_SECTION(50);

  DAC8760_Latch_Low(ch);
  DAC8760_Latch_High(ch);

  EXIT_CRITICAL_SECTION();

  return;
} /* End DAC8760_Out_crc */

As you can see I'm sending the 32 bits which includes the CRC, and the DAC doesn't set the output accordingly.

When I don't enable the CRC in the DAC and therefore only send 24 bits (from a different function that doesn't append the CRC) it works great!! Except for the other devices on the SPI bus which most likely are causing the data to be "mis-aligned" when they are receiving data over the SPI bus or some other phenom that causes the DAC to drop it's output, but that's a different issue I will need to deal with...First the CRC??

Does the above code look like it should work?

Regards,

Mike

Hi Garrett, Yes I set the CRC Enable bit in the DAC, and once the bit is set it appeared that I could no longer communicate with the IC. I do get output and have no trouble with communication as long as I do not enable the CRC. We have made some modifications to the circuit (SPI) removing one of the other devices from sharing the SPI with the DACs. Since then I haven't had time to try the CRC. Maybe I will get some time today. I'll let you know. Thanks for your help. Mike