Code for calculating check codes under MOdBUS RTU

CrcCheck AlgorithmShift Method

Unsigned Short CRC16 (Unsigned char *pbuf,int nlength)

{

Unsigned short wreturn = 0xFFFF;

for (int ndatalen=0;ndatalen<nlength;ndatalen++)

{

wreturn^= (unsigned short) (BYTE (Pbuf[ndatalen]));

for (int nindex=0;nindex<8;nindex++)

{

if (wreturn&0x0001)

{

wreturn>>=1;

wreturn^=0xa001;

}

Else

{

wreturn>>=1;

}

}

}

return Wreturn;

}

Tabular method

Unsigned Short CRC (Unsigned char *p_uidata, int uicrcdatalen)

{

Constant definition

Const unsigned char c_uicrchigh[256] =

{

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40

};

Const unsigned char c_uicrclow[256] =

{

0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06, 0x07, 0xC7, 0x05, 0xC5, 0xc4, 0x04,

0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xc9, 0x09, 0x08, 0xC8,

0xd8, 0x18, 0x19, 0xd9, 0x1B, 0xDB, 0xDA, 0x1A, 0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC,

0x14, 0xd4, 0xd5, 0x15, 0xD7, 0x17, 0x16, 0xd6, 0xd2, 0x12, 0x13, 0xd3, 0x11, 0xD1, 0xD0, 0x10,

0xF0, 0x30, 0x31, 0xF1, 0x33, 0xf3, 0xF2, 0x32, 0x36, 0xf6, 0xf7, 0x37, 0xf5, 0x35, 0x34, 0xf4,

0x3C, 0xFC, 0xFD, 0x3d, 0xFF, 0x3F, 0x3e, 0xFE, 0xFA, 0x3A, 0x3B, 0xFB, 0x39, 0xf9, 0xF8, 0x38,

0x28, 0xe8, 0xe9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA, 0xEE, 0x2e, 0x2F, 0xEF, 0x2D, 0xED, 0xEC, 0x2C,

0xE4, 0x24, 0x25, 0xe5, 0x27, 0xE7, 0xe6, 0x26, 0x22, 0xe2, 0xe3, 0x23, 0xe1, 0x21, 0x20, 0xE0,

0xA0, 0x60, 0x61, 0xa1, 0x63, 0xa3, 0xa2, 0x62, 0x66, 0xa6, 0xa7, 0x67, 0xa5, 0x65, 0x64, 0xa4,

0X6C, 0xAC, 0xAD, 0x6d, 0xAF, 0x6F, 0x6e, 0xAE, 0xAA, 0x6A, 0x6b, 0xAB, 0x69, 0xa9, 0xa8, 0x68,

0x78, 0xb8, 0xb9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA, 0xBE, 0x7E, 0x7F, 0xBF, 0x7d, 0xBD, 0xBC, 0x7C,

0xb4, 0x74, 0x75, 0xb5, 0x77, 0xb7, 0xb6, 0x76, 0x72, 0xb2, 0xb3, 0x73, 0xb1, 0x71, 0x70, 0xb0,

0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92, 0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54,

0x9c, 0x5C, 0x5d, 0x9d, 0x5f, 0x9F, 0x9E, 0x5E, 0x5A, 0x9a, 0x9b, 0x5b, 0x99, 0x59, 0x58, 0x98,

0x88, 0x48, 0x49, 0x89, 0x4B, 0x8b, 0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4f, 0x8d, 0x4d, 0x4C, 0x8c,

0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42, 0x43, 0x83, 0x41, 0x81, 0x80, 0x40

};

unsigned short Uicrchi;

unsigned short uicrclo;

unsigned short uiindex;

Uicrchi = 0xFF;

Uicrclo = 0xFF;

Uiindex = 0;

CRC operation

while (uicrcdatalen--)

{

Uiindex = Uicrchi ^ *p_uidata++;

Uiindex &= 0xFF;

Uicrchi = Uicrclo ^ C_uicrchigh[uiindex];

Uicrchi &= 0xFF;

Uicrclo = C_uicrclow[uiindex];

Uicrclo &= 0xFF;

}

Assemble the results into 16-bit

Uicrchi <<= 8;

Uicrchi + = Uicrclo;

return (Uicrchi);

}

Code for calculating check codes under MOdBUS RTU