# Flip Flops help, I have an exam this Friday! Cramming!!!!!!!

Discussion in 'Homework Help' started by jshakil, May 4, 2015.

1. ### jshakil Thread Starter New Member

May 4, 2015
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Hi, I need help with this problem, (I'm going to be posting a bit more) I don't want any answers, but instead I would like help on how to solve the problem. I have been struggling with this stuff and don't know what to do. So I've decided to come here. Thank you in advance!

2. ### tshuck Well-Known Member

Oct 18, 2012
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675
Since are using a flip flop that is sensitive to the falling clock edge (and assuming the setup and hold times aren't violated*), Q <= D at each falling edge.

So, at each falling edge of the clock signal, what is D? The value of D will be output on Q at the clock transition.

*given the nature of this problem, it is probably safe to assume no setup and hold times for this flip flop.

3. ### jshakil Thread Starter New Member

May 4, 2015
7
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Okay, so I know that D=Q. So at the falling edge of the clock, that's where Q will be whatever D is, right?

4. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
The falling clock edge is the point Q changes to be what D is at that point, yes - Q doesn't change at any other time.

So, Q gets the value of D at the falling edge and holds its value until the next falling clock edge.

5. ### jshakil Thread Starter New Member

May 4, 2015
7
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Okay, awesome! I'm going to put my results in paint, and upload it here for you to look at if that' alright. Thank you tshuck

Last edited by a moderator: May 5, 2015
6. ### jshakil Thread Starter New Member

May 4, 2015
7
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I came up with this...

7. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
That looks right to me, though your question is also asking for the value at t=35ms, which your diagram doesn't seem to account for...

8. ### jshakil Thread Starter New Member

May 4, 2015
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I just submitted the answers and it says they were partially correct. (It doesn't give information on which were correct/incorrect)

I'm going to try this again when I come back from work. I'll let you know. Thank you for your help so far tshuck.

9. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
I would suggest you examine the value of Q at t=35ms...

10. ### jshakil Thread Starter New Member

May 4, 2015
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Ah okay, so that would be 0-->1 for the 35ms.

Oct 18, 2012
3,531
675
Thats it!

12. ### jshakil Thread Starter New Member

May 4, 2015
7
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Thank you, awesome news. I just submitted it and it came out correct. Now on to the next one!