# Ripple counter using d flip flops

Joined Nov 24, 2011
629
Hello
I need help to understand logic of ripple counter. I understand the operation of d flip flops
.

I understand the operation of first flip flop but I don't understand what will output of second and third flip flop

#### ericgibbs

Joined Jan 29, 2010
18,633
The 'D' inputs must be connected to the /Q output in order for the F/F to toggle.
Look at this example image.
Post your explanation of the operation.
E

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#### WBahn

Joined Mar 31, 2012
29,843
Hello
I need help to understand logic of ripple counter. I understand the operation of d flip flops.
I understand the operation of first flip flop but I don't understand what will output of second and third flip flop
Have you even tried?

Draw a square wave for the clock signal into the first DFF. Since you understand the operation of D flip flops, you should have no trouble drawing the output of the first flip flop.

Well, that IS the clock signal for the second flip flop. Since you understand the operation of D flip flops, you should have no trouble drawing the output of the second flip flop.

Well, that IS the clock signal for the third flip flop. Since you understand the operation of D flip flops, you should have no trouble drawing the output of the third flip flop.

Now look at the results. Do they correspond to a counter? Which bit is the msb and which bit is the lsb? Is it running forward or backward?

#### bertus

Joined Apr 5, 2008
22,264
Hello,

How do you manage to produce those very hard to read images?
I have used GIMP to correct the white balance and scaled them down:

Bertus

Joined Nov 24, 2011
629
I think the response of counter should be below
At first raising clock
Input I2,I1,I0=000
Output q2,q1,q0=000
At second raising clock
Input=010
Output=010
At third raising clock
Input=011
Output =011
....... So on
Counter count number 01234567
Am I correct?

#### bertus

Joined Apr 5, 2008
22,264
Hello,

What do you use for the input signal at the D inputs of the flip-flops?
When D does not change, the output will not change.

Bertus

Joined Nov 24, 2011
629
Hello,

What do you use for the input signal at the D inputs of the flip-flops?
When D does not change, the output will not change.

Bertus
I am stuck here. If there is no input data then how to know behavior of counter. I have seen in book. D input should be connected to /Q.
raising edge - output of flip flop will be same as input
Falling edge - output does not change
Clock high- no change
Clock low- no change

#### bertus

Joined Apr 5, 2008
22,264
Hello,

Have a look at chapter 7.6 of the attached PDF.

Bertus

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#### WBahn

Joined Mar 31, 2012
29,843
I think the response of counter should be below
At first raising clock
Input I2,I1,I0=000
Output q2,q1,q0=000
At second raising clock
Input=010
Output=010
At third raising clock
Input=011
Output =011
....... So on
Counter count number 01234567
Am I correct?
You don't have an input to any of the flip flops, so how can you say what the input is?