Shift register implementation of CRC- Please help!

Discussion in 'Homework Help' started by ferrero, May 16, 2009.

  1. ferrero

    ferrero Thread Starter New Member

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    Hi guys... new here

    I have a problem with the following and hope all the gurus here can help me out on this


    Consider a transmission system using Cyclic Redundancy Check (CRC) technique with a
    generator polynomial ​
    10101. The receiver receives the following bit pattern:

    100111011000.
    (a) Draw a digital logic circuit for a shift register implementation of CRC.
    [8 marks]



    (b) Use the logic to evaluate the received bit pattern to see whether the bit pattern
    is error-free.​
    [12 marks]


    thank!:D
     
    #1
  2. hgmjr

    hgmjr Moderator

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    There are a number of very good articles on the Internet that present a solution that uses gates. Here is a pretty thorough article on CRC that covers the subject.

    hgmjr
     
    #2
  3. ferrero

    ferrero Thread Starter New Member

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    :eek: thanks for the link hgmjr!


    so base on that article 10101 = 1*x0 + 0*x1 + 1*x2 + 0*x3 +1*x4

    therefore = 1 + x2 + x4

    but is the circuit like this?


    A<---B + C<---D +




    :confused::confused:
     
    Last edited: May 16, 2009
    #3
  4. ferrero

    ferrero Thread Starter New Member

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    Please help to see if this is correct becoz the 12 mark question is ok for me... juz need to get the circuit right... pls?
     
    #4
  5. hgmjr

    hgmjr Moderator

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    Go ahead and take a stab at drawing up the CRC circuit and post it here. We can then make suggestions on what you need to adjust should a correction be needed.

    hgmjr
     
    #5
  6. hgmjr

    hgmjr Moderator

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    Did you use the "MANAGE ATTACHMENTS" button to attach your diagram?

    hgmjr
     
    #6
  7. ferrero

    ferrero Thread Starter New Member

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    here you go... :D
     

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    #7
  8. hgmjr

    hgmjr Moderator

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    I would imagine that you would need 5 stages rather that just 4, since there are five bits in your CRC term.

    hgmjr
     
    #8
  9. ferrero

    ferrero Thread Starter New Member

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    i look at my coure notes and they only have A B C D for 5 bit 11001

    and this is how they drew it


    can you kindly enlighten me directly??... i am really confused now :confused::confused:

    thanks...
     

    Attached Files:

    #9
  10. hgmjr

    hgmjr Moderator

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    I stand corrected.

    You wrote the correct equation in your earlier post.

    I am used to the flow shown like the article that I linked you to earlier.

    One thing for sure, your vertical arrows should be pointing into the circled + signs rather than the flip/flops.

    hgmjr
     
    #10
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