Delta Electronics AC Drive VFD-F Series User Manual page 88

Step 6: Repeat step 2 to 5 for the next 8-bit byte of the command message.
Continue doing this until all bytes have been 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.
For example, read 2 words from the to address 2102H of AMD with address 01H.
The CRC register content of last byte from ADR to number of data is F76FH. The
command message is as following. 6FH will transmit before F7H.
The following is an example of CRC generation using C language. The function
takes two arguments:
Unsigned char* data
Unsigned char length
The function returns the CRC values 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;
}
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Command message:
ADR 01H
CMD 03H
Data starting 02H
address
02H
Number of data 00H
(word)
02H
CRC CHK Low 6FH
CRC CHK High F7H
a pointer to the message buffer
the quantity of bytes in the message buffer
5-55
VFD-F Series
5