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)?

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
http://forum.allaboutcircuits.com/threads/jk-flip-flops.118483/page-2
reread what I wrote in post #26, and this time pay attention so I don't have to keep repeating myself.

but why is Q in 1 unknown?

 

The flip-flop has no RESET input to put it in a known state. There is no specification for what state the flip-flop is in when power is turned on. The flip-flop cannot change state EXCEPT on the rising edge of the clock. Can you logically determine what state the device is in based on the information you are given. I don't know how you would do that and you have not offered any explanation that your teacher might have secretly communicated to you without our knowledge. So there you are.

 

The flip-flop has no RESET input to put it in a known state. There is no specification for what state the flip-flop is in when power is turned on. The flip-flop cannot change state EXCEPT on the rising edge of the clock. Can you logically determine what state the device is in based on the information you are given. I don't know how you would do that and you have not offered any explanation that your teacher might have secretly communicated to you without our knowledge. So there you are.

Can you give me answer, what is Q? It makes no sense to explain more

 

I did give you part of the answer. Q is unknown up until time period #5. You could not accept or understand why this should be the case. I agree that it makes no sense to explain more. I suggest you walk away from the material for a couple of days, then go visit your instructor during his office hours. Explain your problem to him and ask for his help. He is both trained and paid to help you. I'm just a volunteer and helping you is quite beyond my meager capabilities. It is quite clear to me that giving you the solution won't help you in the slightest, because you won't understand the explanation. Good luck.

 

I did give you part of the answer. Q is unknown up until time period #5. You could not accept or understand why this should be the case. I agree that it makes no sense to explain more. I suggest you walk away from the material for a couple of days, then go visit your instructor during his office hours. Explain your problem to him and ask for his help. He is both trained and paid to help you. I'm just a volunteer and helping you is quite beyond my meager capabilities. It is quite clear to me that giving you the solution won't help you in the slightest, because you won't understand the explanation. Good luck.

You could tell me on begining that you don't know how to solve this. Thank you

 

You could tell me on begining that you don't know how to solve this. Thank you

This tactic won't get you far at all. We have seen it over and over: someone feels entitled to have others do their work for them and, upon discovering that others won't accommodate them, try to trick them into doing so by insinuating that they must not know how to, hoping that the person will feel compelled to prove that they do. It's a childish tactic (though, sadly, it does sometimes work). But it only hurts you in the long run as people that were more than willing to help guide YOUR efforts, simply turn their attention to those that are actually willing to put in some effort of their own.

 

You could tell me on begining that you don't know how to solve this. Thank you

I know how to solve the problem, but I'm retired now after half a century of working at this stuff. I've got nothing left to prove. Good luck with your studies and the learning of languages that are not your first language.

 

I know how to solve the problem, but I'm retired now after half a century of working at this stuff. I've got nothing left to prove. Good luck with your studies and the learning of languages that are not your first language.

 

At the end this is what I get, Is this good or not?

 

As you go from period #4 to period #5, both J and K are HI. What does the output of a JK FF do at the rising clock edge when both control inputs are HI?

 

As you go from period #4 to period #5, both J and K are HI. What does the output of a JK FF do at the rising clock edge when both control inputs are HI?

Toggle

 

Toggle

Correct.

So I have a coin sitting on my desk in front of me. I just flipped it over. Do you now know whether it is heads up or tails up?

 

Correct.

So I have a coin sitting on my desk in front of me. I just flipped it over. Do you now know whether it is heads up or tails up?

You need to check it

 

But I've given you just as much information about this coin as you have about that flip flop as you go from Period #4 to Period #5.

 

But I've given you just as much information about this coin as you have about that flip flop as you go from Period #4 to Period #5.

Ok so how diagram should be between period 4 and 5?

 

It's not defined until #8 right?

 

It's not defined until #8 right?

Correct!