4-Bit Asynchronous Binary Counter stops counting after reset

Thread Starter

JohnnyBravoo

Joined Mar 7, 2020
4
Background:
This about one part of a school assignment for my PLTW Digital Electronics class. I have attached the pdf of the assignment, the multisim files, and a video of the circuit sim if anyone is interested. Basically I need make a "Now Serving Display" (like the ones seen at deli counters) from Asynchronous Counters. The circuit should count up to 80, increasing by one on a button press, on two seven segment displays and then stop once it reaches 80. First we must make the circuit on NI Multisim 14.2 on something called PLD mode and then download the code onto an FPGA and test it on the NI Digital MiniSystem (myDAQ, myDigital Protoboard, and the Cmod S6 FPGA Module).
The issue:
For the ones place display (LSB) we have to use the CNTR_4BIN-AS which is the PLD mode equivalent of the 74LS93 IC. Anyway I have the counter connected to a digital clock, and I have an AND gate inputs connected to the QD (Q3) and the QB (Q1) outputs of the counter, and the AND gate output to the R01 (MR1) and R02 (MR2) so that when the counter reaches 10 it resets the counter and the display only goes up to 9. However, when this reset happens, the counter just stops counting despite the clock input still working. Please help me fix the problem.

The video the chip in question: https://drive.google.com/file/d/1Ws_uQ-PyV1XT-qZFzNEZYpNpugz0DUtj/view?usp=sharing
 

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dl324

Joined Mar 30, 2015
10,462
It would be helpful if you posted a schematic.

Why are you using a binary counter when a decade counter is available?

Post a schematic for the other counter.
 

Thread Starter

JohnnyBravoo

Joined Mar 7, 2020
4
It would be helpful if you posted a schematic.

Why are you using a binary counter when a decade counter is available?

Post a schematic for the other counter.
If you look at the pdf, it basically tells us how to do everything, so that's why I use the binary counter (it is mandated by the assignment). I will attach the schematics to this comment.
Also, I can send you the actual multisim files if that helps at all (I can't attach them here)
 

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dl324

Joined Mar 30, 2015
10,462
If you look at the pdf, it basically tells us how to do everything, so that's why I use the binary counter (it is mandated by the assignment).
So this is some contrived restriction to make the problem a little more complicated. That's fine.
I will attach the schematics to this comment.
The relevant part of your circuit:
1583686449486.png
Also, I can send you the actual multisim files if that helps at all (I can't attach them here)
I don't have Multisim and Mouser no longer has a free version.

BTW, you can force Multisim to make cleaner routes by using the shift key. Otherwise, you can move the wires after they've been placed. Your schematic will be easier to read if you don't run wires over labels (or components).

I don't see a problem with your circuit.

What is the purpose of the OR gate and what is the logic level for BTN1 when you're seeing a problem?

EDIT: MSD counter circuit for future reference:
1583687871950.png
 
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Thread Starter

JohnnyBravoo

Joined Mar 7, 2020
4
So this is some contrived restriction to make the problem a little more complicated. That's fine.
The relevant part of your circuit:
View attachment 200985
I don't have Multisim and Mouser no longer has a free version.

BTW, you can force Multisim to make cleaner routes by using the shift key. Otherwise, you can move the wires after they've been placed. Your schematic will be easier to read if you don't run wires over labels (or components).

I don't see a problem with your circuit.

What is the purpose of the OR gate and what is the logic level for BTN1 when you're seeing a problem?
The BTN1 is supposed to be a manual reset button for both the ones place (the part we're focused on now) and the tens place (the stuff at the top). When I had it hooked up to both counters without the OR gate, the automatic reset signal (The AND Gate thing) from the bottom counter would interfere with the top counter, so I have the OR gate in order to stop the "interference".
The logic level for BTN1 is LOW when the problem occurs.

Also, I have discovered something new. When I remove the OR Gate like this: it works fine. The counter counts up to 9 and then resets again... So it is some problem with the OR gate, however I need the OR gate for the aforementioned reason.
1583688525511.png
Thanks for taking the time to help me!
 

dl324

Joined Mar 30, 2015
10,462
So it is some problem with the OR gate, however I need the OR gate for the aforementioned reason.
Sometimes Multisim gets confused when you rip up and reroute wires. I've had cases where it looked like a wire was connected and it wasn't. When things didn't work as expected, I got in the habit of grabbing components and moving them around to make sure all of the wires were actually connected. In your case, it's something else. As long as the BTN1 input was low, it should have worked.

The problem doesn't mention anything about a worker being able to stop before serving 80 customers. Why would you need to reset the least significant digit (LSD) if it's already at 0?
 

Thread Starter

JohnnyBravoo

Joined Mar 7, 2020
4
Sometimes Multisim gets confused when you rip up and reroute wires. I've had cases where it looked like a wire was connected and it wasn't. When things didn't work as expected, I got in the habit of grabbing components and moving them around to make sure all of the wires were actually connected. In your case, it's something else. As long as the BTN1 input was low, it should have worked.

The problem doesn't mention anything about a worker being able to stop before serving 80 customers. Why would you need to reset the least significant digit (LSD) if it's already at 0?
From the PDF:
"Design a digital circuit that displays the count from 00 to 80. This design has two control
inputs and two output displays. The two inputs are Next and Reset. The Next signal comes
from a push-button switch that, when pressed, advances the display by one. The Reset
signal, which is also a push-button switch, will reset the display to a count of 00.
When the
display reaches 80 the count will cease."
 

dl324

Joined Mar 30, 2015
10,462
The Reset
signal, which is also a push-button switch, will reset the display to a count of 00.
When the
display reaches 80 the count will cease."
If the counter is at 80 and you only reset the MSD, what the count reset to?
 
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