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Sequential Logic

Sequential Logic: Flip-Flops and Registers

When we talk about electronic parts, particularly logic ICs, flip flops and registers are two major components of a sequential logic circuit. This is because of the useful applications they offer. But before diving into their details, it is important that we know exactly what sequential logic is.

Sequential Logic

Sequential logic, according to the Automata theory, is a logic circuit whose output depends on the following two things:

  1. the present input value, and
  2. the input history – sequence of past inputs.

This definition of sequential logic proves that sequential logic is stateful.

Flip Flop

In digital electronic parts, a flip flop is a circuit that has two stable states that are used to store binary numbers. Changing the input can alter the data stored in a flip-flop. It is the basic element for storing information in sequential logic.

Types of Flip Flops

Four types of flip-flops exist in digital electronic parts. These include:

  1. SR Flip Flop
  2. JK Flip Flop
  3. D Flip Flop
  4. T Flip Flop

Applications of Flip Flops

Flip flops have a wide array of applications in electronics. Some of the most common applications are discussed below.


Counters are a widely used electronic component. These sequential circuits are used to count the number of events that occurred in a specific period. Counters are made of flip-flops because they have to remember the past states of a digital circuit.


As mentioned above, flip flops store data in the form of binary numbers, that is 0 and 1. This is a single bit. Registers, on the other hand, are used in the storage of data consisting of more than one bit. Flip flops are connected in a sequence in order to enable registers to store data in “bytes,” which is a bigger unit than a “bit.”

Frequency Division

A frequency divider circuit is used to give a digital signal output half the input frequency. For example, a frequency divider fed 100k Hz of frequency will give an output of 50k Hz. This is called frequency division. Flip flops are the electronic circuits used in frequency dividers to divide the frequency.

Data Transfer

Data transfer from one register to another is called “data transfer.” This is done through shift registers, and flip-flops play a key role in data transfer. There are two types of data transfer:

  1. Serial – one data line is used to transfer one bit of data at a time.
  2. Parallel – multiple data bits over multiple lines at a time.


We have briefly talked about registers in the applications of flip flops. However, there is more to this particular electronic part than meets the eye. As discussed above, registers are a collection of flip flops with the major function of storing binary data.

Significance of Registers in Sequential Logic Circuits

Registers have substantial significance in sequential logic circuits. This is because they not only perform the function of storing data but are able to do the transfer as well. Both of these register functions are discussed below.

Registers as Data Storage Units

A question arises: if both flip flop and registers are essentially performing the same function, why are registers needed in the sequential logic circuits? The answer lies in the amount of data a register is able to store as compared to a flip-flop. While a flip-flop can store only one bit of data, a single register can have n bits of data stored in it, depending on the number of flip-flops it is made up of.

Shift Registers

The difference between a normal and a shift register is that, in a shift register, the stored data can be moved or shifted from one flip-flop to another. The shift register uses a clock signal to perform its data-shifting function. The shifting of data in a register can be done in either direction with the help of a Shift Left Register or a Shift Right Register.

Applications of a Register

Just like flip flops, registers also have a number of different applications depending on how they are used. These include:

Memory Function

The basic function of a register, as mentioned above, is the storage of data. All electronic systems need to store large amounts of data, and registers help in doing exactly that. The amount of data stored in a register depends on the number of flip-flops used in it.

Calculation of Results or Outputs

Applications of registers are not limited to data storage only. Rather, registers can also be used for the calculation of results or outputs. This is done by varying the control signals.

Counting Cycles & Performing Logical Comparisons

Another application of registers is that they are used to count cycles or perform a particular task multiple times. They are also used as Arithmetic Logic Units (ALUs) to perform logical comparisons between numbers or strings.


In a nutshell, flip flops and registers are two important electronic parts of a sequential logic circuit. Both of these electronic components offer a wide array of functions, the most notable of which is the memory function. Other than storing data, they are used in counters, frequency dividers, and the transfer of data.

The same is the importance of registers when it comes to usability. They also have a number of different applications and are even used as Arithmetic Logic Units for logical comparisons.

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