Mod 60 counter with stop start and reset function. Help!

Discussion in 'Homework Help' started by ashmeo, Nov 21, 2011.

  1. ashmeo

    Thread Starter New Member

    Nov 21, 2011
    17
    0
    My assignment is to build a 60 sec stopwatch (mod 60 counter) with a stop(pause), reset(00), and a start (from where it paused) function.

    I'm given 74LS93, 74LS00, 74LS 32 and any other standard logic gates and flip flops as necessary.

    Picture 1: So i built a standard mod 60 counter using mod 10 and mod 6. it counted up to 59 and became 00. Thats what i want.

    Here is a the multisim file which i had done after adding in the features.The problem is that it does not count up anymore. When i simulate it a random number shows but the reset function works as when i push the switch the random number becomes 00. Correct my errors. Thank you :D

    Please state the input and output of any modifications i need to make or better yet upload an image file. thanks!
     
    Last edited: Nov 21, 2011
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Which one is your pause button supposed to be?

    I don't see the logic you followed when you connected the QA output of the decade counter to the NAND gate, along with the clock. It also doesn't makes sense that you connect the NAND output to both CLKA and CLKB of the unit counter.
    It also is a design mistake to connect two outputs together, namely the QA output of the units counter with the output of the NAND gate.

    The datasheet says that you must connect QA to CLKB, just as you did in the first schematic.

    If you want to pause the counting, you just have to AND the Clock pulse with a control signal before it reaching any IC, without meddling with any of the clock circuitry.
     
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