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???
08/13/07 20:40
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 		 #143230 - FYFI
Responding to: ???'s previous message
I suspect you'd like to work things out on paper first, so for your future information, I refer you to this document:

http://www.danlhenry.com/hdlc/hdlcbcc.pdf

That document's section 2.2.5 specifies the 16-bit FCS (CRC) used by the international standard HDLC protocol. In section 4.1, you will find various FCS implementations. The code I posted in your thread here was a slight optimization of Fcs16_b(). Fcs16_b() is an 8-bit optimized version of Fcs16_a(). I refer you to Fcs16_a() because it shows the algorithm in a 'simpler' form for comparison to your pencil and paper work.

List of 32 messages in thread
TopicAuthorDate
CRC16 CCITT - What a challenge!            01/01/70 00:00      
   Have you seen this?            01/01/70 00:00      
      Of course!            01/01/70 00:00      
         Balance            01/01/70 00:00      
            I know, Russ,            01/01/70 00:00      
         Code? What code?            01/01/70 00:00      
            in the code library - look to the left column            01/01/70 00:00      
               Thanks! I missed that note in the first post.            01/01/70 00:00      
   I need a hint            01/01/70 00:00      
      write down the bits            01/01/70 00:00      
         Thanks for the hint            01/01/70 00:00      
            Your observations plus a comparison in C            01/01/70 00:00      
               The rest of the story ...            01/01/70 00:00      
                  Compilers, but Keil C51 8.09 for the stated 28~            01/01/70 00:00      
                  and this processes only a nibble, isn't it...            01/01/70 00:00      
                     No, it process the entire byte.            01/01/70 00:00      
                        now it\'s my pencil time...            01/01/70 00:00      
                           FYFI            01/01/70 00:00      
                              Clarification re: 8-bit optimized term            01/01/70 00:00      
                              on optimisation            01/01/70 00:00      
                                 Jan's optimization            01/01/70 00:00      
                                    Re: on optimization            01/01/70 00:00      
                                       Can you please be more specific?            01/01/70 00:00      
                                          More specifically ...            01/01/70 00:00      
            and what            01/01/70 00:00      
               More on checksums            01/01/70 00:00      
   No reason to hide the excreted code            01/01/70 00:00      
      Excreted code needs context like any other code            01/01/70 00:00      
   One More Comment            01/01/70 00:00      
      ... and a marginal remark ...            01/01/70 00:00      
         Init all ones frequently specified            01/01/70 00:00      
   18 cycles            01/01/70 00:00      

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