What is SR Flip Flop?
- SR flip flop is one of most simplest type of flip flops.
- It stands for Set Reset flip flop.
- It is a clocked flip flop.
Construction of SR Flip Flop-
The clocked SR flip flop can be constructed in two ways-
- By using NOR latch
- By using NAND latch
Way-01: Construction of SR Flip Flop by using NOR latch-
Here, we use a NOR latch and two other AND gates to construct the SR flip flop.
Way-02: Construction of SR Flip Flop by using NAND latch-
Here, we use a NAND latch and two other NAND gates to construct the SR flip flop.
The above table can be reduced as-
|States and Conditions|
|0||0||X||Qn||Hold State condition S = R = 0|
|0||1||X||0||Reset state condition S = 0 , R = 1|
|1||0||X||1||Set state condition S = 1 , R = 0|
|1||1||X||Indeterminate||Indeterminate state condition S = R = 1|
Draw a k map using above truth table-
Qn+1 = ( SR + SR’ ) ( Qn + Q’n ) + Qn ( S’R’ + SR’ )
|Qn+1 = S + QnR’|
We will draw excitation table of any flip flop using its truth table.
What is excitation table?
For a particular combination of present state Qn and next state Qn+1, excitation table tell the inputs required.
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