Up/down Decade counter using D Flipflop

Discussion in 'Homework Help' started by fordelon1, Aug 24, 2011.

  1. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    Hi..
    I do have a question how to do this, it must be a 4bit decade counter.. that counts from 0-99, up and down... and can be reset to 0. All of this using D flip flops
    no luck searching the web, all i can see are JKFF and TFF...

    please, I need your help designing this...
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    You'll need to build two 4-bit decade counters then; as a 4-bit decade counter can only store a number from 0 to 9.

    Here is a Wikipedia entry on flip-flops; the D-type F/F is mentioned:
    http://en.wikipedia.org/wiki/Flip-flop_(electronics)

    An educational site on D-type f/f's:
    http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/dflipflop.html

    A 4000-series CMOS D-type flip flop:
    http://www.nxp.com/documents/data_sheet/HEF4013B.pdf

    A 74-series TTL D-type flip flop:
    http://www.learn-c.com/74ls74.pdf
     
  3. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    thank you for your fast response..
    yes, i know the basic of D flip flop..

    can you give me some of the idea how to start in K-Mapping or building the schematic diagram..

    I appreciate any answer from you sir.
     
  4. keithisdoped

    New Member

    Aug 22, 2011
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    irrelevant!

    good luck:)
     
    Last edited: Aug 24, 2011
  5. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    Thank you for your response,
    but we was instructed to build this circuit strictly using D Flip flop only
    of course with the help of basic logic gates, the clock timer, and the 7447..

    any idea?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    I will get you started on how to make a decade counter, but you will have to do some of the work yourself.

    Firstly, you will need four flip-flops of any kind since you will need four bits for 0-9.
    Next you create a table showing all the possible states you can have with four bits.
    On the next column you write down the next state of the 4-bit counter. For example, 3->4
    When a state is not applicable, write down X to mean "don't care"

    Here is the partial table:

    DCBA DCBA(next state)
    0000 0001
    0001 0010
    0010
    0011
    0100
    0101
    0110
    0111
    1000
    1001 0000
    1010 xxxx
    1011 xxxx
    1100
    1101
    1110
    1111

    I will leave it up to you to fill in the missing lines.

    Next, you need to draw four separate Karnaugh maps, one for each flip-flop
    Take for example, the A-flip-flop. Enter into each of the 16 squares of the map the next state of the A-flip-flop: 0, 1 or X. For example, in state 0000, the next state of A will be a 1. For state 0001, the next state is 0. For state 1010, the next state is X.

    Next step, reduce the Karnaugh map to a boolean equation, and then into a circuit diagram.

    If you have gotten this far, you are doing well.

    To be continued.
     
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  7. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    if x=0; it is an up counter if x=1; it is a down counter.
    Z would be the trigger for the TENS
    PS NS Z

    DCBA x=0 x=1 x=0 x=1
    0000 0001 1001 0 1
    0001 0010 0000 0 0
    0010 0011 0001 0 0
    0011 0100 0010 0 0
    0100 0101 0011 0 0
    0101 0110 0100 0 0
    0110 0111 0101 0 0
    0111 1000 0110 0 0
    1000 1001 0111 0 0
    1001 0000 1000 1 0
    1010 xxxx xxxx x x
    1011 xxxx xxxx x x
    1100 xxxx xxxx x x
    1101 xxxx xxxx x x
    1110 xxxx xxxx x x
    1111 xxxx xxxx x x

    Is my truth table correct?...

    if this is correct, would you please help in simplifying it thru KMApping please..
    more power to you sir..
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Firstly, let's not use x to mean UP/DOWN. Use a different symbol such as DIR.

    I have purposely not included UP/DOWN because I wanted to make sure you understood how to do a simple 0-9 counter first. Also for the same reason let us not worry about the 2-digit counter at this point.

    However, yes, your truth tables for both UP and DOWN are correct.
    Read up first on Karnaugh mapping and then I will show you how to do one.
     
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  9. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    KMAP for A...


    B'A'x' B'A'x B'Ax B'Ax' BAx' BAx BA'x BA'x'

    D'C' 0 1 0 0 0 0 0 0
    D'C 0 0 0 0 1 0 0 0
    DC x x x x x x x x
    DC' 1 0 1 0 x x x x
    (I'm having a difficulty in spacing, but i think you can get this one)
    I'm having a hard time simplifying a Kmap even though I know it's basic concept, can you help me with their KMAP..

    Thank you for your good response sir...
     
  10. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    Sir, If you can allow me,
    can you please post their Individual [4]simplified boolean..

    so i can check and compare my work with yours.
    only if you can allow me sir?

    thank you..
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Nope. You show me your work first.
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    Here is the Karnaugh map for flip-flop "A".

    There are many ways to draw a K-map. If drawn correctly they will all reveal the same solution.

    The important thing to note is - when moving from one square to an adjacent square, only a single bit in the square number changes state - i.e. Gray Code is used.

    Another thing to note is that the map can be visualized as a complex cylinder that can be wrapped around in both the horizontal and vertical axes. For example, square #0 wraps around with square #2 and with square #8.

    [​IMG]

    Now, you show the Karnaugh maps for bits B, C and D. I am not going to do them for you.

    Later I will show you how to reduce the map to the simplest boolean equation and circuit, if you do not already know how to do so.
     
    Last edited: Aug 25, 2011
    anhnha likes this.
  13. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    Thank you for your response MrChips, yes I've done plotting the 4 KMaps, A B C and D...
    my problem is in simplifying the boolean algebra for all of them, it seems that i have a difficulty in grouping variables and simplify them...
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    Do you know how to arrive at a solution for the K-map I have shown?
    Show your work.
     
  15. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    is the answer A' ?... i have a difficulty in simplifying a KMap... the first and fourth column are grouped together...
     
  16. MrChips

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    Oct 2, 2009
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    Yes, that is correct. Now show your work for the other flip-flops.
     
  17. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    but my design has an input which is DIR[specifies up/down counter]... so my variables are
    A, B, C, D and DIR.. i need a 5 variable, a total of 32 blocks in K-map..
     
  18. MrChips

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    Oct 2, 2009
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    Like I said, make sure you can do the simple UP counter first before moving on. Remember, proper learning requires taking one step at a time.
     
  19. fordelon1

    Thread Starter New Member

    Aug 16, 2011
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    B= da'
    c= ca'
    d= cba
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    I did not get the same answers as you did.
     
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