74LS190

Discussion in 'Homework Help' started by Trevis Johnson, Oct 13, 2014.

  1. Trevis Johnson

    Thread Starter New Member

    Oct 13, 2014
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    Is there a way to make the 74LS190 go from only 0-6, or 0-2, instead of 0-9?

    I'd like for the 74LS190 to go from 0-6 then putout a signal and restart again 0-1-2-3-4-5-6(repeat, add count to another display)-0-1-2-3-4-5-6
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    What the truth table look like?
     
  3. Trevis Johnson

    Thread Starter New Member

    Oct 13, 2014
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    I'm not really sure what you mean, truth table of which? The 0-6 or, anything over the pin output of 0110 needs to reset it back to zero and I'm just unsure how to reset it
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    The 7 is 0111, so run pins that output 111 to the AND gate. Run the output of the AND gate to the Reset pin of the chip (if it has one).

    The logic of it is this: when counting 0-6, one of the inputs to the AND gate is going to be 0, so the output of the AND gate is 0. But when you hit 7, the three inputs to the AND gate will be 1, when all inputs to the AND gate are 1, the output of the AND gate is 1 so AND gate goes active ("turns ON"). Since output of the AND gate is connected to reset, when AND gate turn ON, the reset turns ON. And you should start counting from 0 again.

    Check what input reset needs. If it is active high, then all you need is the AND gate as I described. If it is active low, then you need to put NOT gate between AND gate and reset pin.
     
  5. Trevis Johnson

    Thread Starter New Member

    Oct 13, 2014
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    Right right, but I don't know which one is the reset, doesn't even look like there is one which is kinda my problem, so if I have an and gate to reset at 6 where do I place it back at? The clock? Or load (power)? Or somewhere else?
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    The 74LS190 doesn't have a reset, but it does have a parallel load. You can wire the parallel load to act like a reset.

    Ground all the parallel inputs, P0 thru P3. Then, since the parallel load is active low, wire the output of the AND gate through a NOT gate to the parallel load input.
     
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  7. Trevis Johnson

    Thread Starter New Member

    Oct 13, 2014
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    Oh this is fantastic, I'll try this tomorrow!! Thank you thank you
     
  8. Papabravo

    Expert

    Feb 24, 2006
    10,145
    1,791
    You can decode any value that you want AND parallel load any value that you want. This creates many interesting sequences on the four outputs.
     
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