CRC Cyclic Redundancy Check

[achaccha]

Dear Friends. I need your valuable help understanding the CRC (cyclic redundancy check) in a given file.
I say this because I have had several cases as to make immo off Audi or VW, the engine turns on but the scan says: Eprom Error.
I also had trouble changing the VIN number in Mitsubishi, the scanner can see the new VIN number but reading error codes says: Eprom error.
I've been looking and this is due to the CRC, I hope someone can provide more information about it or at least if someone can provide bibligrafia and so to understand the calculation of cyclic redundancy "CRC"
thanks

[speedy100]

Hi,

Check this site out. They have a freeware program for what You need.
IRNIS on the NET - home of Advanced CheckSum Verifier - the MD5SUM, MD5 and SFV utility for Windows. (http://www.irnis.net/?prod=xcsc&ver=1.0.0)

B.R.

[KriptoKey]

Hello Friends.
Please if anyone can explain in more detail about the CRC (Cyclic Redundancy Check).
I have understood that when a change is made in a dump byte of the CRC also varies. can someone tell how to calculate the CRC.
The example is for audi immo off, changing 02 instead of 01 the CRC is modified and therefore have to change 6F 6E And instead of 70 and 6F.
please i need to know how to do this calculation.
20 20 20 20 20 5A FF 04 08 30 35 31 30 30 37 5A
05 01 02 00 0C AD 00 00 00 00 69 C1 00 A5 6F FD
05 01 02 00 0C AD 00 00 00 00 69 C1 00 A5 6E FD

20 20 20 20 20 5A FF 04 08 30 35 31 30 30 37 5A
05 01 01 00 0C AD 00 00 00 00 69 C1 00 A5 70 FD
05 01 01 00 0C AD 00 00 00 00 69 C1 00 A5 6F FD

thanks

[achaccha]

You're absolutely right friend, these bitz in a dump must meet an addition or subtraction.
these bitz not be changed at the whim of any number, must meet a logic. I recently tried to clean the dump of a VW and I came out when scanning fault codes that relate to the CRC.
0002 - Internal Control Module Memory Check Sum Error B2000 00 [137] - Lower Limit Exceeded Freeze Frame: Fault Status: 00000001 Fault Priority: 1 Fault Frequency: 1 Mileage: 0 km Date: 2009.14.08 Time: 00:00:24

0104 - Internal Control Module Memory Check Sum Error B2000 00 [137] - Implausible Signal Freeze Frame: Fault Status: 00000001 Fault Priority: 1 Fault Frequency: 1 Mileage: 0 km Date: 2009.14.08 Time: 00:00:24

I hope someone can enlighten us on this issue so we can learn and make changes to the Dump taking into account the CRC.
thanks