CRC
Enviado: 03 Mai 2010 08:28Estou tentando montar um crc modbus mas não estou conseguindo, estou seguindo este padrão, a função gera um crc mas meus programas de teste e o clp não aceita este crc!
alguem tem alguma idéia do que está faltando? estou usando o MikroC.
o crc precisa atender este padrão mas sou fraco em C não entendo-o completamente!
A procedure for generating a CRC is:
1, Load a 16–bit register with FFFF hex (all 1’s). Call this the CRC register.
2. Exclusive OR the first 8–bit byte of the message with the low–order byte
of the 16–bit CRC register, putting the result in the CRC register.
3. Shift the CRC register one bit to the right (toward the LSB), zero–filling the
MSB. Extract and examine the LSB.
4. (If the LSB was 0): Repeat Step 3 (another shift).
(If the LSB was 1): Exclusive OR the CRC register with the polynomial
value A001 hex (1010 0000 0000 0001).
5. Repeat Steps 3 and 4 until 8 shifts have been performed. When this is
done, a complete 8–bit byte will have been processed.
6. Repeat Steps 2 through 5 for the next 8–bit byte of the message.
Continue doing this until all bytes have been processed.
7. The final contents of the CRC register is the CRC value.
8. When the CRC is placed into the message, its upper and lower bytes
must be swapped as described below.
alguem tem alguma idéia do que está faltando? estou usando o MikroC.
- Código: Selecionar todos
unsigned short CRC16 ( puchMsg, usDataLen ) /* The function returns the CRC as a unsigned short type */
unsigned char *puchMsg ; /* message to calculate CRC upon */
unsigned short usDataLen ; /* quantity of bytes in message */
{
unsigned char uchCRCHi = 0xFF ; /* high byte of CRC initialized */
unsigned char uchCRCLo = 0xFF ; /* low byte of CRC initialized */
unsigned uIndex ; /* will index into CRC lookup table */
while (usDataLen--) /* pass through message buffer */
{
uIndex = uchCRCLo ^ *puchMsgg++ ; /* calculate the CRC */
uchCRCLo = uchCRCHi ^ auchCRCHi[uIndex} ;
uchCRCHi = auchCRCLo[uIndex] ;
}
return (uchCRCHi << 8 | uchCRCLo) ;
}
o crc precisa atender este padrão mas sou fraco em C não entendo-o completamente!
A procedure for generating a CRC is:
1, Load a 16–bit register with FFFF hex (all 1’s). Call this the CRC register.
2. Exclusive OR the first 8–bit byte of the message with the low–order byte
of the 16–bit CRC register, putting the result in the CRC register.
3. Shift the CRC register one bit to the right (toward the LSB), zero–filling the
MSB. Extract and examine the LSB.
4. (If the LSB was 0): Repeat Step 3 (another shift).
(If the LSB was 1): Exclusive OR the CRC register with the polynomial
value A001 hex (1010 0000 0000 0001).
5. Repeat Steps 3 and 4 until 8 shifts have been performed. When this is
done, a complete 8–bit byte will have been processed.
6. Repeat Steps 2 through 5 for the next 8–bit byte of the message.
Continue doing this until all bytes have been processed.
7. The final contents of the CRC register is the CRC value.
8. When the CRC is placed into the message, its upper and lower bytes
must be swapped as described below.