how the output of flip flop is determine by the input (truth table)

[ronsimpson]

what does it mean that nothing will change no function

If Clock = 0 then Q can not change.
>Q=Q Q is stored, can not change, will not change
>D does not change anything. Q=Q, can not change, Nothing happens, No function.
>How do I say 'nothing can happen'.

If Clock = 1 then Q can not change.
>Same as above. Nothing can happen.

If Clock = falling edge then Q can not change.
>Q can not change. No function.
>>>No AND function.
>>>No OR function.
>>>No XOR function.
>>>No Invert (1/x).
>>>Nothing happens. Q=Q No change.

In the above examples D=x. It does not mater what D is.
>>If D=1 or If D=0 all the above is still true.

If Clock =_/ then Q becomes what D is.
>>>This is the only time D can effects Q.
>>>This is the only case where anything happens. This is a function.

D Clk |Q
--------------
0 0 | Q
1 0 | Q
0 1 | Q
1 1 | Q
0 _/| 0
1 _/| 1

Because the top 4 lines have the same results (q=q) then it does not matter what D or Clk are. They can be anything and the same thing happens. (nothing)
D Clk |Q
--------------
x x | Q

I don't know how to tell you Q=Q.
>>If Q=0 before, Then Q=0 after.
>>If Q=1 before, Then Q=1 after.
>>>>>Q=Q
>>>>>Qold=Qnew
>>>>>Q=Qn

This flip flow is "memory". You can write something into memory only on the rising edge of clock.
What is written is D.
Once something is stored it can not be changed (if power is on) until some thing new is written.
The reason I say Q=? is because when you get memory (or a hard drive) you don't know what the person before you wrote in the memory. If you don't know what is in memory then Q=?. Only after you put something known into memory can you say Q=1 or Q=0.

 

[Parth86]

If Clock = 0 then Q can not change.
>Q=Q Q is stored, can not change, will not change
>D does not change anything. Q=Q, can not change, Nothing happens, No function.
>How do I say 'nothing can happen'.

If Clock = 1 then Q can not change.
>Same as above. Nothing can happen.

If Clock = falling edge then Q can not change.
>Q can not change. No function.
>>>No AND function.
>>>No OR function.
>>>No XOR function.
>>>No Invert (1/x).
>>>Nothing happens. Q=Q No change.

In the above examples D=x. It does not mater what D is.
>>If D=1 or If D=0 all the above is still true.

If Clock =_/ then Q becomes what D is.
>>>This is the only time D can effects Q.
>>>This is the only case where anything happens. This is a function.

D Clk |Q
--------------
0 0 | Q
1 0 | Q
0 1 | Q
1 1 | Q
0 _/| 0
1 _/| 1

Because the top 4 lines have the same results (q=q) then it does not matter what D or Clk are. They can be anything and the same thing happens. (nothing)
D Clk |Q
--------------
x x | Q

I don't know how to tell you Q=Q.
>>If Q=0 before, Then Q=0 after.
>>If Q=1 before, Then Q=1 after.
>>>>>Q=Q
>>>>>Qold=Qnew
>>>>>Q=Qn

This flip flow is "memory". You can write something into memory only on the rising edge of clock.
What is written is D.
Once something is stored it can not be changed (if power is on) until some thing new is written.
The reason I say Q=? is because when you get memory (or a hard drive) you don't know what the person before you wrote in the memory. If you don't know what is in memory then Q=?. Only after you put something known into memory can you say Q=1 or Q=0.

thank you for the explain i know i can make counter memory registers with the help of d flip flop
first I want learn the basic concept of counter how to make counter with the help of d flip fliop
I want to count only two number i know i need display, d flip but don't know how many flip flop are i need to make counter does any circuit i need to use like adder, encoder i don't want to explain whole process I just want how to make counter after learn about the flip flop

 

[MikeMl]

The reason I define Clk=1 as a clock event is because then you can discuss any kind of flip flop, be it positive edge triggered, negative edge triggered,or level actuated (a latch), Clock active high or active low. You just have to note what type of clock it takes, and the truth table, present state-next state table becomes universal. Think of clock event = 0 as meaning "the Clk signal has not met the requirement to be a clock", and "clock event = 1 as meaning "the Clk signal has met the requirement to be a clock"

Now, why did I put eight states in my table? I did it to drive the point home that when characterising a flop, again in the general case, there would be eight possible combinations of three things which could (possibly) influence what the next state of the flop will become.

In a Dflop (a specific type of flop), some of the pairs of rows can be grouped together by recognising that the next state is independent of some of the inputs, so the input which doesnt matter can be replaced with an X (dont care). That doesn't change the fact that there are eight combinations of D, Clk, and Qn