SR Flip Flops

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-

  1. By using NOR latch
  2. 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.

 

Logic Circuit-

 

 

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.

 

Logic Circuit-

 

 

Logic Symbol-

 

 

Truth Table-

 

INPUTSOUTPUTS
SRQn

(Present State)

Qn+1

(Next State)

0000
0011
0100
0110
1001
1011
110Indeterminate
111Indeterminate

 

The above table can be reduced as-

 

INPUTSOUTPUTSREMARKS
SRQn

(Present State)

Qn+1

(Next State)

States and Conditions
00XQnHold State condition S = R = 0
01X0Reset state condition S = 0 , R = 1
10X1Set state condition S = 1 , R = 0
11XIndeterminateIndeterminate state condition S = R = 1

 

Characteristic Equation-

 

Draw a k map using above truth table-

 

 

Qn+1 = ( SR + SR’ ) ( Qn +  Q’n ) + Qn ( S’R’ + SR’ )

Qn+1 = S + QnR’

 

Excitation Table-

 

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.

 

QnQn+1SR
000X
0110
1001
11X0

 

 

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Summary
SR Flip Flops
Article Name
SR Flip Flops
Description
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. The clocked SR flip flop can be constructed in two ways- By using NOR latch and By using NAND latch
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Gate Vidyalay
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