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Tuesday, September 22, 2015

Flipflops

FLIP FLOPS
·         A flip flop is a sequential loic device used to store one bit information. It is also called as bi-stable device since it has two possible states: 1 (high) and 0 (low).

Types of flip flops:
1.       RS flip flop.
2.       Clocked RS flip flop.
3.       D flip flop
4.       J-K flip flop.
5.       T flip flop.

RS flip flop:
·         RS flip flop has two inputs labelled S and R. The two outputs are labelled Q and Q. In flip flops the outputs are always complementary. In other words, if output Q =1, then output Q=0, and so on. The letters R and S are often referred as set and reset inputs.


                                                

  Truth table
S
R
Q(n+1)
Comments
0
0
Qn
No change
0
1
0
Reset
1
0
1
Set
1
1
x
Not allowed
·        
A  high S (S=1) and low R (R=0) results in the set state (Q=1).
·         A low S (S=0) and high R (R=1) results in the reset state (Q=0).
·         When both inputs are low (S=0, R=0), results in no change in output(Q= lastvalue).

·         When both inputs are high (S=1, R=1), results in indeterminate state and this is known as race condition.

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