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Jan Waclawek
08/04/07 17:33
Modified:
  08/04/07 17:42

Read: 791 times
Bratislava
Slovakia


 
#142771 - I said it\'s simple
Responding to: John Myers's previous message
once you have that "online calculator" page... (my favourite)0

OK it's not simple because there is so many buzz around, and everybody uses different nomenclature and different algorithm and stuff. Even the word, "polynome", it's completely misleading - it refers to a very weird sort of arithmetics, not what normal people are normally using, but nobody tells you this.

In the last few years I was forced to go through the same procedure four or five times to implement various protocols, every time the calculation was different, all kinds of stuff - look at that page, there are many boxes to click and fill in, these are those damn'd variants of CRC and you never know that the perverse person who devised the protocol decided to reverse the bits or use the "nondirect" version or a nonzero initial value - or all of these...

OK so go to that page and follow my instructions:
  • CRC order - 8 (i.e. CRC8)
  • CRC polynom - 07 (the "1" in your 0x107 is the bit you feed back from the xors - normal people don't use it in the number determining the "polynom" as this is implicit from the algorithm, but some pervert people like to add it so that it confuses the normal people - in your case some really naughty guy even added an extra zero, so this looks as a 16-bit poly rather than 8-bit... but don't believe them, this is 8-bit only, hence 0x07)
  • initial/final value - both 0
  • set the "direct" algorithm
  • untick both "reverse" tickboxes
  • into data sequence, enter %00, click "compute!" you have the first item to the table; into data sequence, enter %01, click "compute!", you have the second item to the table, etc. - you get the idea by now I hope


JW

PS. The table for the nibble method is simply the first 16 items from the "standard" table



List of 23 messages in thread
TopicAuthorDate
How to create a crc table?      John Myers      08/04/07 02:33      
   simple      Jan Waclawek      08/04/07 08:10      
      RE: simple      John Myers      08/04/07 15:34      
         I said it\'s simple      Jan Waclawek      08/04/07 17:33      
            Thank you      John Myers      08/04/07 18:27      
            Protocols      Andy Neil      08/06/07 07:48      
               examples      Jan Waclawek      08/06/07 08:05      
   Runtime Computed Table??      Michael Karas      08/04/07 09:14      
      RE: Runtime...?      John Myers      08/04/07 16:02      
      table is not necessary      Jan Waclawek      08/04/07 17:41      
         Benchmark      John Myers      08/04/07 18:16      
            I did benchmarks as such on AVR      Michael Karas      08/04/07 19:38      
               Similar findings      Russell Bull      08/04/07 21:05      
                  no beavers that I've tended to!!      Michael Karas      08/04/07 22:50      
               not bitwise....      Jan Waclawek      08/05/07 02:45      
            Better is a strong word      Neil Kurzman      08/05/07 21:19      
               Also comment about SMBus PEC Code...      Michael Karas      08/05/07 21:30      
   The Table      Neil Kurzman      08/06/07 11:19      
   The Nibble Table for Poly 107      Neil Kurzman      08/06/07 11:20      
   The formula      Neil Kurzman      08/06/07 11:22      
   Have you seen this?      Richard Erlacher      08/06/07 18:42      
      Now I have      Neil Kurzman      08/06/07 21:26      
      Yes, that is a Key Document!      Andy Neil      08/07/07 02:45      

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