Need helping designing a n up/down counter

Thread Starter

Vertapple

Joined Apr 2, 2022
6
Hello

I have a practical this Monday and urgently need too design a 4-bit up/down counter with D flip flops with very limited gates. I was told to essentially merge an up counter and down counter that I had created (attached below). My own reasoning and examples online indicate the best way to merge these would be with a multiplexer made from the NAND gates but I only have 4 and I believe I need a minimum of 7.
below are my simulations, my working UP counter, working DOWN counter and all available components for the UP/DOWN counter. (ignore the unused connections that are grounded, the simulator is fussy about it).

Any help would be appreciated, thank you
 

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Papabravo

Joined Feb 24, 2006
18,422
Just make one kind of counter, complement the outputs to make the other kind. Now use a multiplexer to select which group of four outputs you want.
 

Thread Starter

Vertapple

Joined Apr 2, 2022
6
Just make one kind of counter, complement the outputs to make the other kind. Now use a multiplexer to select which group of four outputs you want.
OH yes, you're right. Sorry I was making it more complicated than it needed to be. Thank you I'll try it now.
 

dl324

Joined Mar 30, 2015
14,462
Is that the way they're teaching you to draw schematics? I can't make any sense of them.
design a 4-bit up/down counter with D flip flops with very limited gates
What does very limited gates mean?
I was told to essentially merge an up counter and down counter that I had created (attached below).
Why wouldn't they have you design one counter that did both? It wouldn't take more than half an hour or so.
 

Thread Starter

Vertapple

Joined Apr 2, 2022
6
Is that the way they're teaching you to draw schematics? I can't make any sense of them.
What does very limited gates mean?
Why wouldn't they have you design one counter that did both? It wouldn't take more than half an hour or so.
No we draw schematics standardly but this is a simulator that uses IC packages instead of logic gates. as for limited gates you'll see the flip NAND IC (7400) only has 4 sets of inputs and 4 outputs (hence 4 NAND gates) which is limited in the way you can only make 1 2-1 mux before running out. As for why, I couldn't tell you, I'm just following the instructions I need to get the marks.
 

Thread Starter

Vertapple

Joined Apr 2, 2022
6
Just make one kind of counter, complement the outputs to make the other kind. Now use a multiplexer to select which group of four outputs you want.
I tried too do this and I hit another stop, I get to the MUX and now end up with a single bit that decides whether it operates in up or down mode which is ok. Now, however, I have a total of 8 bits (4 of the original and their complements), 2 available AND gates and a way to choose up and down. I'll attach a picture for you to do with what you will.
 

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dl324

Joined Mar 30, 2015
14,462
No we draw schematics standardly but this is a simulator that uses IC packages instead of logic gates.
That's one crappy simulator. I'd hate to have to debug something with it.

You should post schematics that we can read so we can see what you have to work with.
As for why, I couldn't tell you, I'm just following the instructions I need to get the marks.
I designed the counter in half an hour. It took another half an hour to simulate it. I made two mistakes. Wrote down one term wrong and missed one term for one of the counters. It took 28 gates plus the flip flops.
 
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Thread Starter

Vertapple

Joined Apr 2, 2022
6
That's one crappy simulator. I'd hate to have to debug something with it.

You should post schematics that we can read so we can see what you have to work with.

I designed the counter in half an hour. It took another half an hour to simulate it. I made two mistakes. Wrote down one term wrong and missed one term for one of the counters. It took 28 gates plus the flip flops.
yes, I don't really get to decide the simulator so I do whatever they want, I don't really use it enough to complain. But I did end up making a final circuit after realizing a major error in my down counter, after fixing it the answer was basically instantly clear.
 
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