Tag: sr flip flop using nand gate

SR Flip Flop | Diagram | Truth Table | Excitation Table

Flip Flop-

 

Before you go through this article, make sure that you have gone through the previous article on Flip Flops.

 

We have discussed-

  • A Flip Flop is a memory element that is capable of storing one bit of information.
  • It is also called as Bistable Multivibrator since it has two stable states either 0 or 1.

 

There are 4 basic types of flip flops-

 

 

In this article, we will discuss about SR Flip Flop.

 

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-

 

There are following two methods for constructing SR flip flop-

 

 

  1. By using NOR latch
  2. By using NAND latch

 

1. Construction of SR Flip Flop By Using NOR Latch-

 

This method of constructing SR Flip Flop uses-

  • NOR latch
  • Two AND gates

 

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

 

 

To gain better understanding about Flip Flops in Digital Logic,

Watch this Video Lecture

 

Next Article- SR Flip Flop

 

Get more notes and other study material of Digital Design.

Watch video lectures by visiting our YouTube channel LearnVidFun.