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roby

help mistery checksum

2 posts in this topic

hello,

I am studing a serial comunication and I have this :

00010002 e5 63 02 00 ba 0f

In Decimal:

001 048 048 048 049 048 048 048 050 002 101 053 054 051 048 050 048 048 098 097 048 102 004

First byte is SOH , last EOT and that in middle is STX...

Well, anyone know how to determinate last two byte (ba 0f). they are a checksum. crc 16 ??? and perhaps a autoit script to calculate it?

Thank

roby

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Depends on where it came from. CRC-16 is not specific enough. From Wikipedia - Cyclic redundancy check:

Commonly used and standardized CRCs

CRCs as used in globally standardized telecommunications systems have not been fully standardized. Most CRCs in current use have some weakness with respect to strength or construction. Standardization of CRCs would allow for better designed CRCs to come into common use.

* The definition of CRC-12 is disputed, as there are 3 forms of CRC-12 in common use.

* Both forms of CRC-8 in use have notable weaknesses mathematically.

* It is assumed that at least other 10 forms of CRC-16 and CRC-32 exist, but no form of CRC-16 or CRC-32 in use is mathematically optimal.

* CCITT CRCs differ from ITU CRCs (of the same size), as the same entity has standardized checksums more than once but in different eras.

* The ITU and IEEE have been historically helpful in standardizing checksums used in telecommunications equipment and protocols -- but have provided little to no support in standardization since the end of the Cold War.

* These hex values of "Initial value" and "Reflected value" are important for some more complicated checksums (like most forms of CRC-32 and CRC-64).

* CRCs less than CRC-16 do not tend to use Initial or Reflected values.

* Very often custom versions of checksums are created by changing these values, as it does not alter the overall mechanics (or math) of the checksum algorithm -- and may provide some nominal security features.

:)


Valuater's AutoIt 1-2-3, Class... Is now in Session!For those who want somebody to write the script for them: RentACoder"Any technology distinguishable from magic is insufficiently advanced." -- Geek's corollary to Clarke's law

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