CRC problem when using C code

[john2020]

CRC problem

hi all,



I have used this C code posted by others in the forum. But i found that i can only do CRC for 7 bytes. Is it the problem of only 16 elements in the feedback array? or why?


/****************************************************************************
*
* NAME: Crc8()
* PURPOSE: Generate 8-bit CRC.
*
* SYNOPSIS: unsigned char Crc8(unsigned char b, unsigned char initCrc);
*
* INTERFACE PARAMETERS:
*
* Name FG-IO Description
* ------------------- ----- -----------------------------------------
* b F I Data byte to CRC (MSBit first).
* initCrc F I Initial CRC or CRC accumulator for
* continuation.
* <return value> O CRC.
*
* DESCRIPTION:
*
* The function returns the 8-bit CRC after including "b" with the
* initial CRC "initCRC".
*
****************************************************************************/

static const UCHAR code feedback[16] =
{
0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D
};

UCHAR CRC8(UCHAR b, UCHAR CRC)
{
CRC = (CRC << 4) ^ feedback[((CRC) ^ b) >> 4];
CRC = (CRC << 4) ^ feedback[((CRC >> 4) ^ b) & 0x0F];
return (CRC);
}

By the way, i hope to do CRC for 256 byte data and i just input 0xFF for the initial CRC. Is there anything wrong?


regards
john

 

[moorthi]

Re: CRC problem

Hi the code
CRC = (CRC << 4) ^ feedback[((CRC >> 4) ^ b) & 0x0F];

will give only one hex output and more over can you pl post the origianl code which used to calculate the CRC for 7-bytes. cos the polynomial in the calculation may be different

 

[john2020]

Re: CRC problem

hi moorthi

By the way, i hope to do CRC for 256 byte data and i just input 0xFF for the initial CRC.i don' t really know,whether there is any mistake in doing so?i will try to send u code for CRC for 7 bytes of data.have you tried implementing CRC-32bit or CRC-16bit?if so,tel me.

regards
john