# JK Flip flop skizze

Discussion in 'Homework Help' started by thexy, Dec 14, 2015.

1. ### thexy Thread Starter Member

Dec 13, 2015
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0

It's given time course of the inputs. I need to circle is Q 1,0 or not known (unbekannt). Can someone help me with this example?

Mod edit: reduced image size (after WBahn did it below) to reduce loading times.

Last edited by a moderator: Dec 14, 2015
2. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
Let's first see about getting your image to a reasonable size and orientation:

Next, you need to show YOUR best attempt to solve YOUR problem.

Take it one step at a time.

For slot 1, do you know what the state of the flip flop is?

Dec 13, 2015
126
0
No :/

4. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
I think I misread your intent. I thought you were refusing to answer the question, when in fact I think you WERE answering the question.

That is correct, you do not know what the initial state of the flip flop is.

That's fine -- that's one of the three options available to you. So now go on to step #2.

5. ### thexy Thread Starter Member

Dec 13, 2015
126
0
What is step 2?

6. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
The step after step 1.

I'm referring to time slot #2 (you already have #1 done and there are a total of 12).

7. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
BTW: What does "Zeitabschnitt" translate to? Time slot? Time period?

8. ### thexy Thread Starter Member

Dec 13, 2015
126
0
But I don't know where should go 0,1 or not known

9. ### thexy Thread Starter Member

Dec 13, 2015
126
0
Time course/period

10. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Hint: A flip-flop changes it's state ONLY on the rising edge of the clock (CLK).

11. ### thexy Thread Starter Member

Dec 13, 2015
126
0
Is Q 001unknown001001unknown0

12. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Q is unknown until the first rising clock edge which occurs in period #5. The value of Q in period #5 depends on the values of J, K, and possibly Q in period #4 according to the work you did on understanding the state machine diagram.

13. ### thexy Thread Starter Member

Dec 13, 2015
126
0
Still don't understand

14. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
1. When the clock signal (CLK) is HIGH, the output Q cannot change.
2. When the clock signal (CLK) is LOW, the output Q cannot change.
3. When the clock signal (CLK) has a falling edge (a transition from HIGH to LOW), the output Q cannot change.
The clock signal has it's first rising edge (a transition from LOW to HIGH), at the beginning of period #5

Therefore Q must be unknown in periods #1, #2, #3, and #4 because it was unknown in time period #1, and it has not changed.
Just before the rising edge at the beginning of time period #5, J=K=1 which means that when the rising clock edge arrives the flip-flop will do what?
Choose one of the following:
1. Clear to 0
2. Set to 1
3. Do nothing
4. Toggle
If your answer is 1 or 2 then you know the value of Q. If your answer is 3 or 4, then you still don't know and you must proceed to the next step. which time period has the next rising edge of the clock (CLK)?

15. ### thexy Thread Starter Member

Dec 13, 2015
126
0
How I know that in period 5 J and K=1

16. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
You look at the diagram.
1. In time period #5, J is clearly higher than it is in time period #6
2. In time period #5, K is clearly higher than it is in time period #3
To me the diagram is showing quite clearly the values 0 and 1, true and false, high and low. What did you think the diagram was showing?

17. ### thexy Thread Starter Member

Dec 13, 2015
126
0
Same, but i just started learning flip flops so it's still unclear to me. So J is 1 until period 6 or?

18. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Yes.
1. J=1 for periods 1 through 5
2. J=0 for periods 6 through 8
3. J=1 for periods 9 through 12
Similarly for K and CLK.

19. ### thexy Thread Starter Member

Dec 13, 2015
126
0
Ok I understand that. Can you explain me how to get value ofQ?

20. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
See post #14 in this thread. The values of J and K just before the rising clock edge determine the value of Q according to the state machine that you analyzed in your previous thread on the JK state machine. I wrote out the behavioral description of what happens when J and K assume certain values. Go back to that previous thread