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74LS193 counter issue - Please help

Discussion in 'Electronics Homework Help' started by CKaiL, Oct 10, 2014.

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  1. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    Hi

    I am trying to let it count down from 10 to 0 and stop at 0. However , when I run it on multisim , it doesn't run at all. Anyone knows the issue? or did i connect wrongly? Please guide me
     

    Attached Files:

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    It looks like the CLR input is not connected to anything. With TTL and LS logic devices, unconnected inputs assume the high state. This will hold the counter reset. You need to tie the CLR input to 0V.

    Inputs should not be left unconnected. Any other inputs you're not using should be tied to appropriate logic levels.
     
  3. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    Hi
    Thanks for your reply. It is now able to run but it is not able to start at 10. It starts at 15 instead and then to 0 an repeat
     

    Attached Files:

  4. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    You need to load your '10' value before you begin the count.
    You have also connected the 'up' input to Vcc, was this intentional, or did you want that grounded?
     
  5. CKaiL

    CKaiL

    12
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    Oct 10, 2014
    May I know how do I load "10" value?
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    You need a momentary 'Low' on the Load pin to input the values you have setup on the 'input' side of the counter.
     
  7. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    Hi
    When I connect the the load to ground (low) , it is able to display the A (value 10). However , it just remains there.It doesn't count down at all.
     

    Attached Files:

  8. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Remove the load to ground connection after the counter is loaded. See @Gryd3 post #6. It is a momentary connection.
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    And read the data sheet. Read it again. Read it until you understand it!
     
  10. Gryd3

    Gryd3

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    Jun 25, 2014
  11. CKaiL

    CKaiL

    12
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    Oct 10, 2014
    How do I set up a momentary 'Low' to the load of 74LS193?
     
  12. Gryd3

    Gryd3

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    Jun 25, 2014
    Using a momentary push button to begin the count-down, or toying around with a capacitor and resistor to hold the load pin low for a moment when you first power your circuit.
     
  13. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    Hi
    Thanks for your reply. I am able to do it now except maybe one more thing from me. How do I stop it at 0? Meaning when it counts from 9....3,2,1,0 then stop. I am thinking to use the clear function.

    Currently , it will continue to count from 9.... 3 ,2 ,1 ,0 then back to 15 to 0.
     
  14. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    I tried connecting the output ABCD to nand gate then to clear function of the IC. However , when i run the program , 7 segment shows nothing not even a 0. May I did something wrong again. Please advise me. Thank you
     
  15. Gryd3

    Gryd3

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    Jun 25, 2014
    Did you take a look at that data sheet?
    The sample input/outputs will show you that there is a pin that changes state when the counter hits 0. If you can find it, you can use it to stop the count
     
  16. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    I am not sure if I have look correctly. When the clear function is set to high , Output of ABCD will all be low regardless of load , data and count input.

    I did try connect to it to the 74LS193 using a 4input NOR gate but 7 segment display nothing not even a 0 .

    I use NOR gate because when Qabcd are all 0 , it will trigger a 1 and clear the 7 segment making it 0. Not sure if my logic is correct.

    Please correct me if I am wrong or any mistake that I have made. Thank you
     
  17. Gryd3

    Gryd3

    4,098
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    Jun 25, 2014
    When the device first turns on, all of the outputs are low, so your nor will tie the clean pin high before your counter even begins.
    Have you seen the 'Borrow' pin?
     
  18. CKaiL

    CKaiL

    12
    0
    Oct 10, 2014
    Hi
    I managed to get the count to stop at 0 now with the help of borrow pin. However, I still don't really understand how it work in the datasheet. When the borrow pin is low , it triggers a high for Qabcd?

    Thank you for your help
     

    Attached Files:

  19. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Nope. When the counter is at 0, and is told to count down again, it wraps around and starts at 15 again (Which is binary 1111)
    The borrow pin is an output, that can be used when cascading more counters together... so what one counter hits 0, and is told to go down again, the borrow pin could make the next counter in the circuit count down.
    The carry pin is the same thing, but will make the next counter count up when it's at 15 and told to go up again... without, it would go up to 15, overflow, and count 'up' to 0 again.

    (Similar to how 80 becomes 79... the 10's position needs to decrease when the 1's position needs to count down below 0. The 1's position borrows from the 10's position)
     
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