Difference Between SR Flip – flop and RS Flip – flop

The flip-flop is nothing but a term that lies under digital electronics which is an electronic component that is used to store one bit of information.

As we know Flip Flop is a sequential circuit, its input is based upon two parameters named as the current input and the output from the previous state. It has two outputs; both are complements of each other. It may be in one of two stable states, either 0 or 1.

In this article, we will study the difference between SR and RS flip-flops.

SR Flip-flop

An SR flip-flop (Set-Reset flip-flop) is a fundamental digital electronic circuit element used to store and manipulate data. It is a sequential circuit. A sequential circuit is a type of digital circuit in electronics that contains memory units to store and propagate information, and its output depends on both current inputs and internal state.

SR flip flops can be constructed using an SR latch. A latch is a digital electronic circuit with a simple form of memory element, which can store a single bit of binary information (0 or 1).

Methods to Construct SR Flip-flop

There are two methods through which we can construct SR Flip-flop given below :

• SR Flip-Flop using NAND Gate
• SR Flip-Flop using NOR Gate

SR Flip-flop using NAND Gate

SR Latch (Using NAND Gate)

Logic Table of SR Latch

S	R	Q(n+1)
0	0	Invalid
0	1	1
1	0	0
1	1	Hold

SR Flip-flop using NAND Gate

SR Flip-flop (Using NAND -Gate)

Truth Table for SR Flip-flop

Clock	S	R	Q(n+1)
Not Trigger	X	X	Q(n)
Trigger	0	0	Hold
Trigger	0	1	0-Reset
Trigger	1	0	1-Set
Trigger	1	1	Invalid

SR Flip-flop using NOR Gate

SR Latch using NOR Gate

Logic Table for SR Latch using NOR Gate

S	R	Q(n+1)
0	0	Hold
0	1	0
1	0	1
1	1	Invalid

SR Flip-flop using NOR Gate

Logic table for SR Flip-Flop using NOR Gate is same as SR Flip-Flop using NAND Gate.

SR Flip-flop (Using NOR Gate)

RS Flip-flop

The Basic building blocks of RS Flip-flop is same as SR Flip-flop:

RS Flip-flop

Logic Table

S	R	Q
0	0	Hold
0	1	0
1	0	1
1	1	Invalid

Difference between SR and RS Flip-Flop

In RS Flip-Flop, Reset input has high priority i.e. RS Flip-Flop resets the output. RS (Reset-set) Flip-Flop will be RESET (0).

In SR Flip-Flop, Set input has high priority i.e. SR Flip-Flop sets the output. SR (Set-Reset) Flip-Flop will be SET (1).

• SR Flip-Flop

When the result Q = S or (note : not R and Q)

inputs are marked S1 (priority set input) and R (reset input)

S = 0 and R = 0 → Q = Q (unchanged)

S = 0 and R = 1 → Q = 0 (reset)

S = 1 and R = 0 → Q = 1 (set)

S = 1 and R = 1 → Q = 1 (set is dominant)

• RS Flip-flop

When the result Q = not R and (S or Q)

inputs are marked R1 (priority reset input) and S (set input)

S = 0 and R = 0 → Q = Q (unchanged)

S = 0 and R = 1 → Q = 0 (reset)

S = 1 and R = 0 → Q = 1 (set)

S = 1 and R = 1 → Q = 0 (reset is dominant)

Difference Table on SR and RS Flip-Flop

Characteristics	SR Flip-flop	RS Flip-flop
S = 0, R = 0	No change in Q state (Hold).	No change in Q state (Hold)
S = 0, R = 1	Reset (Q = 0)	Reset (Q = 0)
S = 1, R = 0	Set (Q = 1)	Set (Q = 1).
S = 1, R = 1	set (dominant) (Q = 1)	Reset (dominant) (Q = 0)
Dominance:	When both S and R are 1, the set operation dominates	When both S and R are 1, the reset operation dominates

Applications of RS Flip-Flop

RS Flip-Flop are data storage device used to store binary information. It is mainly used in the devices which requires binary information. It is used in:

• Asynchronous Counters (RS Flip-Flop are used in building the asynchronous counters ).
• Shift Registers (RS Flip-Flops can be used to build shift registers).
• State Machines.
• Debouncing Circuit (used in stabilizing output of a switch/button).

Applications of SR Flip Flop

• Register: SR Flip-Flop is used to create a register. Designers can create any size of register by combining SR Flip Flops.
• Counters: SR Flip-Flops used in counters. Counters count the number of events that occur in a digital system.
• Memory: SR Flip-Flops are used to create memory which is used to store data when the power is turned off.

Frequently Asked Questions

1. How many RS Flip-Flops are required to store 10 bit data values ?

To store a 10-bit binary data value, we would need 10 RS flip-flops. Since a single RS flip flop will store a single binary digit. In order to store 10 bit data value we need 10 RS flip-flops.

2. Which flip-flop kind is more stable in terms of glitch prevention?

RS flip-flops are considered to be more stable than SR flip-flops because when they are used in edge triggered configuration, they do not provide the error.

3. What role do clock signals play in RS and SR Flip-Flops?

Clock signals are frequently used with RS and SR flip-flops to govern when the inputs might alter the flip-flop’s state. This aids in the avoidance of race situations and the proper running of consecutive circuits.