Tag: sr flip flop table

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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