Flip flop with feedback input

Discussion in 'Homework Help' started by vead, Sep 5, 2016.

  1. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    Hello
    I have doubt. Please Look at work,
    _20160905_200940.JPG
    actually I have connected to flip flops to make counter, so that I can understand work of both flip. I have doubt for second flip flop, please look at table of second flip flop. Output of first flip flop goes to input of second flip flop. Does table of second flip flop follow that condition?
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,877
    370
    The fourth line of your F1 table is incorrect. It should be the same as the second line.
    As F1 and F2 are identical circuits their truth tables will be identical too.
     
  3. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    Yes that is my mistake, now output of first flip flop is 1010, it should be input for second flip flop. Means clock high low high low is it right?
     
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,877
    370
    Yes
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Two things -- you don't need to document what happens when the clock falls low because we already knew what happens -- nothing.

    Second, you say that you've built the circuit. What does it actually do?

    Doing tables for F1 and F2 separately is all fine and dandy -- and as noted by AlbertHall they should look identical because they are the same circuit -- but what you need is a table the shows the output of the circuit, namely Q1 (the Q output of F2) and Q0 (the Q output of F1) that result from successive rising clock edges (starting with Q1 = Q0 = 0). THAT is the output of your counter. Then you can compare it to the output you actually see on the actual circuit. You should discover something interesting -- namely that your counter is running backwards.
     
  6. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    I looked timing diagram, now I understand behavior of counter
    Q0=1010
    Q1=1100
    O=3210
    Thank you very much
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Good!

    So now see if you can DESIGN it so that it runs forward. Don't guess. MAKE it do what YOU want it to do.
     
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