ThingMagic M5e-Compact - Manual (Page 57)

Reader-to-Host Communication
Overview of the Communication Protocol 57
An example implementation of CRC calculation, taken from the Arbser source CrcUtils.c,
is shown here:
/** @fn void CRC_calcCrc8(u16 *crcReg, u16 poly, u16 u8Data)
* @ Standard CRC calculation on an 8-bit piece of data. To make it
* CCITT-16, use poly=0x1021 and an initial crcReg=0xFFFF.
*
* Note: This function allows one to call it repeatedly to continue
*
calculating a CRC. Thus, the first time it's called, it
* should have an initial crcReg of 0xFFFF, after which it
* can be called with its own result.
*
* @param *crcRegPointer to current CRC register.
* @param poly
Polynomial to apply.
* @param u8Datau8 data to perform CRC on.
* @return None.
*/
void CRC_calcCrc8(u16 *crcReg, u16 poly, u16 u8Data)
{
u16 i;
u16 xorFlag;
u16 bit;
u16 dcdBitMask = 0x80;
for (i=0; i<8; i++)
{
// Get the carry bit. This determines if the polynomial should be
// xor'd with the CRC register.
xorFlag = *crcReg & 0x8000;
// Shift the bits over by one.
*crcReg <<= 1;
// Shift in the next bit in the data byte
bit = ((u8Data & dcdBitMask) == dcdBitMask);
*crcReg |= bit;
// XOR the polynomial
if (xorFlag)
{
*crcReg = *crcReg ^ poly;
}
// Shift over the dcd mask
dcdBitMask >>= 1;
}
}