16F876 & SHT71

[mce91]

Hello

I has fought for 2 days to make the calculation of the CRC between a SHT71 and a PIC16F876.
Even with the scope note from sensirion I do not arrive there

http://www.sensirion.com/images/getFile?id=80

The calculation of the CRC at sensirion is not standard. I found at DALLAS a scope note (27) which uses the same principle but within sight of the table of CRC from Dallas the result is different.

My crontrainte is not to be able to use a table of CRC (no more place available)

If you have ideas or solutions I am taking
@+

Michel

[MikeValencia]

[mce91]

[mce91]

After lot of hours ... the solution by my self !!!

unsigned int8 crc_sht (char *data,unsigned char oldcrc, unsigned int8 length)
{
unsigned int8 i=0, ibit=0, c=0, crc;


#bit crc4 = crc.4
#bit crc5 = crc.5
#bit crc7 = crc.7
#bit c7 = c.7

crc=oldcrc;
data++;

for (i = 0; i < length; i++, data--)

{
c = *data;
for (ibit = 0; ibit < 8; ibit++)
{
if (c7 == crc7)
{
crc = crc << 1;
crc = crc & 0xFE;
}
else
{
crc = crc << 1;
crc4 = ~(crc4) ;
crc5 = ~(crc5) ;
crc = crc | 0x01;
}
c = c << 1;
}
}
return crc;
}