# Digital logic designing a counter with jk flip flops only don't care ks

Discussion in 'Homework Help' started by 0Wafi0, Jun 3, 2015.

1. ### 0Wafi0 Thread Starter New Member

May 15, 2015
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I've been preparing myself for the exam and I'm trying to design a binary counter using jk flip flops. now the problem is that on one of the k-maps I've got only don't care k's so I'm not sure what the equation for K would be in that case :S

2. ### tshuck Well-Known Member

Oct 18, 2012
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675
A state table with all don't cares doesn't sound like a meaningful circuit. Could you elaborate on what this is and how you got it?

You can group don't cares however you'd like - including/excluding them in whichever way makes your logic simpler.

3. ### WBahn Moderator

Mar 31, 2012
18,085
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We're not mind readers. You need to show us what you've got and what you are trying to do before we can provide much in the way of meaningful feedback.

4. ### 0Wafi0 Thread Starter New Member

May 15, 2015
25
0
my scanner's broken but I'll try my best to explain. I'm supposed design a three bit binary counter using jk flip flops in the sequence from 000 to 111. Once the counter reaches 111 it's supposed stay at 111. so for the control of A I can see that I have a fundamental J so it's good for my equation for J. but for K I only have don't cares. if you'd look at the transition table for the jk flip flops you can see that to have a fundamental K you'd need the out put to go from 1 to 0...now for A that doesn't happen in this sequence as when the counter reaches 111 it stays there without A going back to 0.

5. ### 0Wafi0 Thread Starter New Member

May 15, 2015
25
0
here is the question.

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6. ### WBahn Moderator

Mar 31, 2012
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What is this A that you speak of? Again, we are NOT mind readers! And what is a "fundamental J" or a "fundamental K"?

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7. ### WBahn Moderator

Mar 31, 2012
18,085
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I think I see what you are trying to get at, but engineering is not about guessing. In large part it is about communicating ideas about problems and solutions.

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8. ### 0Wafi0 Thread Starter New Member

May 15, 2015
25
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I am so sorry. for making it so confusing...But I figured it out now. what the questions ask is for equations for the inputs of the three bits counter using jk flip flops...where the method we use are using k-maps and the transition table for jk flip flops to implement this whole circuit. The control of A means the input for the flip flop that will output A. so to find the minimised equation for that I was a little bit stuck... anyway turns out that it's just 0

9. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
I'm glad you figured it out, particularly since you are still speaking in cryptic terms that you won't adequately define, namely you still don't define what output A is. You have three bits and, presumably, three flip flops. One of them apparently outputs a signal called A. Which one? The msb? The lsb? The one in the middle? You need to stop making people guess what you mean. Do you think your customers/employers are going to tolerate that for very long?