Chapter 4 Description of Parameters | VFD-VJ
4-66
Step 1: Load a 16-bit register (called CRC register) with FFFFH.
Step 2: Exclusive OR the first 8-bit byte of the command message with the low order byte of the 16-bit CRC
register, putting the result in the CRC register.
Step 3: Examine the LSB of CRC register.
Step 4: If the LSB of CRC register is 0, shift the CRC register one bit to the right with MSB zero filling, then
repeat step 3. If the LSB of CRC register is 1, shift the CRC register one bit to the right with MSB zero
filling, Exclusive OR the CRC register with the polynomial value A001H, then repeat step 3.
Step 5: Repeat step 3 and 4 until eight shifts have been performed. When this is done, a complete 8-bit byte
will be processed.
Step 6: Repeat step 2 to 5 for the next 8-bit byte of the command message. Continue doing this until all
bytes are processed. The final contents of the CRC register are the CRC value. When transmitting
the CRC value in the message, the upper and lower bytes of the CRC value must be swapped, i.e.
the lower order byte will be transmitted first.
The following is an example of CRC generation using C language. The function takes two arguments:
Unsigned char* data a pointer to the message buffer
Unsigned char length the quantity of bytes in the message buffer
The function returns the CRC value as a type of unsigned integer.
Unsigned int crc_chk(unsigned char* data, unsigned char length)
{
int j;
unsigned int reg_crc=0Xffff;
while(length--){
reg_crc ^= *data++;
for(j=0;j<8;j++){
if(reg_crc & 0x01){ /* LSB(b0)=1 */
reg_crc=(reg_crc>>1) ^ 0Xa001;
}else{
reg_crc=reg_crc >>1;
}
}
}
return reg_crc; // return register CRC
}
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