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

#### jshakil

Joined May 4, 2015
7
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!

#### tshuck

Joined Oct 18, 2012
3,534
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.

#### jshakil

Joined May 4, 2015
7
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?

#### tshuck

Joined Oct 18, 2012
3,534
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?
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.

#### jshakil

Joined May 4, 2015
7
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.
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

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#### jshakil

Joined May 4, 2015
7

I came up with this...

#### tshuck

Joined Oct 18, 2012
3,534
View attachment 85156
I came up with this...
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...

#### jshakil

Joined May 4, 2015
7
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...

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.

#### tshuck

Joined Oct 18, 2012
3,534
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.
I would suggest you examine the value of Q at t=35ms...

#### jshakil

Joined May 4, 2015
7
Ah okay, so that would be 0-->1 for the 35ms.

#### tshuck

Joined Oct 18, 2012
3,534