# Sequential Circuits: Overview Flip Flop Working

flip flop digital electronics are a part of the same in Sequential Circuits.

A sequential Circuit is a type of circuit that consists of an input unit, computational circuit, and output unit.

It is a type of circuit that has output values largely dependent upon the finite past state values and current input values.

The past values are provided by the output feedback loop to the input circuit.

This is because the internal memory elements stored in their system, are capable of storing binary information either in 1 or 0.

Sometimes, memory elements are referred to as excitation or excitation states. The computational circuit can be a type of combinational logic unit, working in two ways

As input
1. Accepts Digital Signal inputs from external devices.
2. Accepts Digital Signal inputs from outputs of memory elements.

As Output
1. Generates Digital Signals as external outputs.
2. Generates Digital Signals as inputs to memory elements.

Applications
There are many systems in which digital outputs must be generated sequentially with the received input digital signals.

A combinational circuit or logic gate is incapable of providing such outputs.
They are used in

• Shift Registers.
• Counters.
• Integrated Circuits.
• Programmable Logic Control.
• VLSI & FGPA.

## What is a Flip Flop? flip flop working

A flip flop in electronics is an electronic circuit that allows two possible stable states to store binary data.

These stable states may occur due to their internal network of combinational circuits mainly NAND, NOR, and NOT gates and the feedback loops.

The binary information stored is either 0 or 1.

Flip Flop, latches, and master-slave are sometimes used for one another, but however, all of them are different from each other.

Flip Flop is a single-clocked/synchronous memory unit.

Mostly, flip flop working in electronics are referred to as Gated Latches.

Latches don’t have any clock signals.

Master Slave is a group of two or more two Flip Flops.

All Flip Flops are made using Logic Gates NAND, AND, NOR, and NOT Gates.

Here, we have used NAND gate, so we should know about its Truth Table

 A B Y=‾AB‾ 0 0 1 0 1 1 1 0 1 1 1 0

## Types of Flip Flops – flip flop working

Flips are mainly categorized into 4 types

1. SR FF (Set Reset Flip Flop)
2. JK FF (Jack Kilby Flip Flop- the inventor)
3. D FF (Data or Delay Flip Flop)
4. T-Type FF ( Toggle Flip Flop)

#### 1) SR Flip Flop

An SR Flip Flop or Set-Reset flip flop is powered by a clock signal, called CLK or ENABLE.

This clock signal is always 1.

If it is 0, the Flip Flop becomes a Latch, or you can say that its output doesn’t change.

Let us look at the flip-flop circuit diagram of this type. ## Case 1: S=0, R=0

S=0, the output of NAND Gate 1 will be S’=1

R=0, the output of NAND Gate 2 will be R’=1

This makes both the outputs of NAND gates 1 and 2 equal to 1.

The input fed into NAND Gates 3 and 4 is now 1.

The next state of NAND Gate 3 or Output Qn could be either 0 or 1, dependent upon the S’ and the next state of NAND Gate 4 as inputs.

The next state of NAND Gate 4 or Output Qn+1 could be either 0 or 1, dependent upon the R’ and the next state of NAND Gate 3 as inputs.

These feedback loops are driven by Don’t care inputs which are denoted by ‘X’.

Don’t care can either be 0 or 1, but unspecified.

Let us suppose

Q=0, Q’=1

For the condition Q=0 to occur,

Input to NAND GATE 4 or Qn+1 must be 1.

Qn+1=1

This makes Qn=0.

For the condition Q’=1 to occur,

Input to NAND Gate 3 or Qn must be 0.

Qn=0

This makes Qn+1=1.

Q=1, Q’=0

For the condition Q=1 to occur,

Input to NAND GATE 3 or Q must be 0.

Qn=0

This makes Qn+1=0.

For the condition Q’=0 to occur,

Input to NAND Gate 4 or Qn+1 must be 0.

Qn+1=0

This makes Q’=0

This condition is referred to as No Change in electronics.

If we observe this practically, one of the outputs is high and another one is low at the same time in accordance with Boolean Laws.

### Case 2: S=0, R=1

S=0, the output of NAND Gate 1 will be S’=1

R=1, the output of NAND Gate 2 will be R’=0

According to the Truth Table of NAND Gate, the output of NAND gate 4 will be 1 as R’=0 is the input,

the other input bit could either be 0 or 1 with the output being 1.

This makes Qn=1.

Qn is being fed as an input into NAND gate 3.

S’=1 and Qn=1 will make the output of NAND gate 3 equal to 0.

Hence, Qn+1=0

So, Q’=0 and Q=1.

This condition is known as the Reset Condition.

It is seen as Resetting the Flip Flop.

### Case 3: S=1, R=0

S=1, the output of NAND Gate 1 will be S’=0

R=0, the output of NAND Gate 2 will be R’=1

According to the Truth Table of NAND Gate, the output of NAND gate 3 will be 1 as S’=0 is the input,

the other input bit could either be 0 or 1 with the output being 1.

This makes Qn+1=1.

Qn+1 is being fed as an input into NAND gate 4.

R’=1 and Qn+1=1 will make the output of NAND gate 4 equal to 0.

Hence, Qn=0

So, Q’=1 and Q=0.

This condition is known as the Set Condition of SR flip flop digital electronics.

It is seen to Set the Flip Flop.

### Case 4: S=1, R=1

S=1, the output of NAND Gate 1 will be S’=0

R=1, the output of NAND Gate 2 will be R’=0

According to the Truth Table of NAND Gate, the output of NAND gate 3 will be 0 as S’=1 is the input,

the other input bit could either be 0 or 1 with the output being 1.

This makes Qn+1=1.

Qn+1 is being fed as an input into NAND gate 4.

R’=0 and Qn+1=1 will make the output of NAND gate 4 equal to 1.

Hence, Qn=1

So, Q’=1 and Q=1.

This condition is known as the Race condition Indeterminate condition or Toggle Mode.

This mode is not allowed as it contradicts the operation of Boolean Laws about flip flops in electronics.

Both the outputs should complement each other, one should be High and one should be Low.

In a practical situation, both High outputs are observed simultaneously.

Eventually, in a few minutes, one of the outputs falls low as this condition is unstable.

This makes SR Flip Flop a Bistable Multivibrator.

Truth Table of SR Flip Flop – flip flop working

 CLK S R S’ R’ Qn+1 Qn Q’ Q Comment 1 0 0 1 1 1 0 1 0 No Change 1 0 0 1 1 0 1 0 1 No Change 1 0 1 1 0 0 1 0 1 Reset 1 1 0 0 1 1 0 1 0 Set 1 1 1 0 0 1 1 1 1 Not Allowed

#### 2) JK Flip Flop – flip flop working

Jack Kilby, the inventor of the first Electronic calculator is the creator of this universal Flip Flop, the Jack-Kilby Flip Flop, abbreviated as the JK FF.

The JK Flip Flop can be easily converted to other types of gated latches by changing connections.

JK Flip Flop is a type of SR flip flop in electronics with additional inputs and an output feedback loop. Case 1: J=0, K=0

The Clock signal is always 1.

For this condition, the output of NAND gate A will be 1, S’=1,

According to the flip flop circuit diagram, the output of NAND gate B will also be 1, R’=1 according to 0 being input as per as NAND operation.

Let us suppose Q=0, Q’=1

For Q=0 to occur, the input to NAND gate C must be 1, making Q’+1=1.

For Q’=1 to occur, the input to NAND gate D must be 0, making Q+1=0.

There is no change in the state.

Let us suppose Q=1, Q’=0

For Q=1 to occur, the input to NAND gate C must be 0, making Q’+1=0.

For Q’=0 to occur, the input to NAND gate D must be 1, making Q+1=1.

There is no change in the state.

Case 2: J=0, K=1

The Clock signal is always 1.

For this condition, the output of NAND gate A will be 1, S’=1,

The output of NAND gate B will be 0, R’=0 according to the NAND operation.

As R’=0, the output of NAND gate D would be high Q’+1=1.

This would happen by low output of NAND gate C, Q+1=0.

This makes Q=0, Q’=1.

This model is referred to as Reset Mode.

Case 3: J=1, K=0

The clock signal is always 1.

For this condition, the output of NAND gate A will be 0, S’=0,

The output of NAND gate B will be 1, R’=1 according to the NAND operation.

As S’=0, the output of NAND gate C would be high Q+1=1.

This would happen by low output of NAND gate D, Q’+1=0.

This makes Q=1, Q’=0.

This model is referred to as Set Mode.

Case 4: J=1, K=1

The Clock signal is always 1.

For this condition, the output of NAND gate A will be 0, S’=0,

The output of NAND gate B will also be 0, R’=0 according to the NAND operation.

For S’=0, the output of NAND gate C would be high Q+1=1.

For R’=0, the output of NAND gate D would be high Q’+1=1.

This makes both the next states high,

Q=1, Q’=1.

Contradicting Boolean Laws, this condition is known as the ‘Toggle’ or ‘Race Around’ condition.

However, it is different from SR FF indeterminate as practically, it is seen that the Flip Flop sets and then, resets.

This means Flip Flop fluctuates from On to Off.

Truth Table of JK Flip Flop

 CLK J K S’ R’ Q+1 Q’+1 Q Q’ Comment 1 0 0 1 1 0 1 0 1 No Change 1 0 0 1 1 1 0 1 0 No Change 1 0 1 1 0 0 1 0 1 Reset 1 1 0 0 1 1 0 1 0 Set 1 1 1 0 0 1 1 1 1 Not Allowed
##### Master-Slave JK Flip Flop
• JK Flip Flop mostly operates as a part of Master-Slave flip flops in electronics.
• Master-Slave Operation means one of the Flip Flop, termed as Master, controls another associated Flip Flop, termed as Slave.
• The clock signal is directly fed to the Master and is fed to the Slave via an inverter, meaning when Master and Slave would operate in opposite cycles.
• Input J and K are directly fed to the Master and the outputs of the Master, Q, and Q’ are fed as J and K inputs to the slave.
• The Master Flip Flop operates during the positive clock cycle and remains latched during the negative clock cycle.
• The Slave Flip Flop operates during the negative clock cycle and remains latched during the positive clock cycle.

Case 1: J=0, K=0

Master-Slave will have no change in their states.

Case 2: J=0, K=1

Master Flip Flop would be reset during the positive clock cycle and Slave Flip Flop would be reset during the negative clock cycle.

Case 3: J=1, K=0

Master Flip Flop would be set during the positive clock cycle and Slave Flip Flop would be set during the negative clock cycle.

Case 4: J=1, K=1

Master Flip Flop would toggle the output during the positive clock cycle and Slave Flip Flop would be fed the toggled output during the negative clock cycle.

The Slave Flip Flop either gets latched or does not operate.

Truth Table of Master-Slave JK Flip Flop

 J K Master Positive Clock Pulse Master Negative Clock Pulse Master Comment Slave Positive Clock Pulse Slave Negative Clock Pulse Slave Comment 0 0 1 0 No Change 0 1 No Change 0 1 1 0 Reset 0 1 Reset 1 0 1 0 Set 0 1 Set 1 1 1 0 Toggle 0 1 Toggle

3) D flip flop working

D or Data flip flop digital electronics is a single bit that is fed to S and R terminals of a modified version of SR Flip Flop.

D is directly fed to S and is inverted when fed to the R terminal of SR Flip Flop.

D Flip Flop is the only Flip Flop that doesn’t operate in Toggle mode.

It is either known as Delay Flip Flop because the inverter might cause a delay. Case 1: When D=0,

S=0, R=1

This will Reset the Flip Flop with outputs being Q=0, Q’=1.

Case 2: When D=1,

S=1, R=0

This will set the Flip Flop with outputs being Q=1, Q’=0.

Truth Table of D flip flop working

 CLK D S R Q Q’ Comment 1 0 0 1 0 1 Reset 1 1 1 0 1 0 Set

### 4) T-Type Flip Flop

T-Type or simply, T flip flop in electronics is a single bit that is fed to J and K terminals of a modified version of JK Flip Flop.

As the name suggests, the T or Toggle Flip Flop can have either 0 or 1 input bits. Case 1: T=0, J=0 and K=0

This state is again, a no-change state.

Case 2: T=1, J=1, and K=1

The output Toggles make the clock signal from positive to negative.

Truth Table of T-Type Flip Flop

 CLK T J K Q Q’ Comment 1 0 0 0 0 0 No Change 1 0 0 0 1 1 No Change 1 1 1 1 0 1 Toggle 1 1 1 1 1 0 Toggle

# What is flip flop explain with an example?

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs.

# Where is flip flop working used?

So flip flops are used to design Registers. According to digital electronics, a Register is a device that is used to store information. As a single flip-flop is allowed for 1–bit storage, n flip-flop working are connected in an order to store n bits of data

# What are the 3 types of flip flop working?

“low” flops with two or three low cards ( or lower) “wet” flops with coordinated cards providing flush and/or straight draws (or made flushes or straights) “dry” flops with uncoordinated cards providing no draws.

# What is the flip-flop working principle of SR flip-flop?

The simplest way to make any basic single-bit set-reset SR flip-flop is to connect together a pair of cross-coupled 2-input NAND gates as shown, to form a Set-Reset Bistable also known as an active LOW SR NAND Gate Latch so that there is feedback from each output to one of the other NAND gate inputs.

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