At 09:03 PM 2/10/00 -0800, you wrote:
>I was searching through the PICLIST archive for a CRC-16
>routine for a project but found nothing useful. The only
>thing I found was a Dallas app note (#27) that uses a
>linear method, no table lookup and no loops.
>

Here is how I did it.  It is a bit of a brute force method and not all that
efficient on the PIC's, but it works.  I use locals because my compiler
doesn't like to dereference pointers in complex statements.  If I used a
global buffer array I think it would be a bit more efficient, but since I
am currently using only 10% of my CPU flash, I just don't care.  :)

typedef struct
{
        uns8 low_byte;
        uns8 high_byte;
} byte_word;

typedef union
{
        uns16 word;
        byte_word bytes;
} word_apart;

word_apart crc;

void crc16_lsb(unsigned char *pData, unsigned char length)
{
    unsigned char i, data;

    crc.word = 0xFFFF;

    do
    {

        data =   *pData;
        pData++;
        crc.bytes.low_byte = crc.bytes.low_byte ^ data;

        for (i = 8; i > 0; i--)
        {
                if (crc.bytes.low_byte & 0x01)
                {
                crc.word = (crc.word >> 1);
                crc.bytes.low_byte = crc.bytes.low_byte ^ 0x08;
                crc.bytes.high_byte = crc.bytes.high_byte ^ 0x84;
            }
            else
                crc.word >>= 1;
        }
    }
    while (--length);

    crc.word = ~crc.word;
}
Erik Reikes
Software Engineer
Xsilogy, Inc.

ereikes@xsilogy.com
ph : (858) 535-5113
fax : (858) 535-5163
cell : (858) 663-1206