74LS193 counter issue - Please help

[CKaiL]

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

 

[KrisBlueNZ]

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.

 

[CKaiL]

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

 

[Gryd3]

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?

 

[CKaiL]

May I know how do I load "10" value?

 

[Gryd3]

You need a momentary 'Low' on the Load pin to input the values you have setup on the 'input' side of the counter.

 

[CKaiL]

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.

 

[hevans1944]

Remove the load to ground connection after the counter is loaded. See @Gryd3 post #6. It is a momentary connection.

 

[KrisBlueNZ]

And read the data sheet. Read it again. Read it until you understand it!

 

[Gryd3]

http://susta.cz/fel/74/pdf/74LS193.pdf

Take a look at page 6. It give you some example inputs/outputs

 

[CKaiL]

How do I set up a momentary 'Low' to the load of 74LS193?

 

[Gryd3]

How do I set up a momentary 'Low' to the load of 74LS193?

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.

 

[CKaiL]

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.

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.

 

[CKaiL]

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

 

[Gryd3]

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

 

[CKaiL]

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

 

[Gryd3]

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?

 

[CKaiL]

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

 

[Gryd3]

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)

 

[tubicochito]

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

how do you manage to get it to stop at 0?