Shift register implementation of CRC- Please help!

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

  1. ferrero

    Thread Starter New Member

    May 16, 2009
    5
    0

    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
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    211
    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
     
  3. ferrero

    Thread Starter New Member

    May 16, 2009
    5
    0
    :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
  4. ferrero

    Thread Starter New Member

    May 16, 2009
    5
    0
    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?
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    211
    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
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    211
    Did you use the "MANAGE ATTACHMENTS" button to attach your diagram?

    hgmjr
     
  7. ferrero

    Thread Starter New Member

    May 16, 2009
    5
    0
    here you go... :D
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    211
    I would imagine that you would need 5 stages rather that just 4, since there are five bits in your CRC term.

    hgmjr
     
  9. ferrero

    Thread Starter New Member

    May 16, 2009
    5
    0
    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...
     
  10. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    211
    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
     
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