# NOR Gate Truth Table | Nor Gate Circuit Diagram

By BYJU'S Exam Prep

Updated on: September 25th, 2023

The NOR gate is a digital logic gate that implements logical NOR. A HIGH output (1) results if both the inputs to the gate are LOW (0); if one or both input is HIGH (1), a LOW output (0) results. NOR is the result of the negation of the OR operator.

The NAND gate and NOR gate are called Universal gates because they can perform all the three basic functions of AND, OR, and NOT gates. This article is about the NOR gate, its truth table, circuit diagram and other details.

Table of content

## What is NOR Gate?

The NOR gate is one of the universal gates. A NOR gate combines an OR gate and a NOT gate. So we can say it is an OR-NOT operation. It may have two or more inputs and an output.

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### NOR Gate Symbol

The logical symbols of the NOR gate are shown:

### NOR Gate Logical Expression

The logical expression for the output is

_     _     __
A + B = AB

It is clear from the truth table that the output is ‘1’ only if all the inputs are at logic ‘0’. It can also say that if the inputs A’ = B’ = 1, the output Y is 1. Thus, the NOR gate is equivalent to the AND gate with inverted inputs, and it can be realized by a bubbled AND gate, as shown above.

## Circuit Diagram of NOR Gate

• The NOR gate is also called the active LOW AND gate.
• The switching circuit of a NOR gate is as shown:

When any of the switches, either A or B, is closed, the bulb will not glow.

NOR gate follows the commutative law as follows:

___    ___
A+B = B+A

However, it does not follow the associative law.

## Enable and Disable Inputs

For a NOR Gate

If control = 0;

 A Control Y 0 0 1 1 0 0

Thus, logic ‘0’ enables input.
If control = 1;

 A Control Y 0 1 0 1 1 0

Thus, logic ‘1’ is disabled input.

## Realization of the Logic Gate – Using NAND Gate and NOR Gate

### NOT Gate Realization

#### Using NOR gate

For the NOT gate realization, we require 1 NOR gate, as shown in the circuit diagram:

### AND Gate Realization

#### Using NOR gate

For the AND gate realization, we require 3 NOR gates if the inputs are not available in complement form, as shown in the circuit diagram:

### OR Gate Realization

#### Using NOR gate

For the OR gate realization, we require 2 NOR gates, as shown in the circuit diagram:

### EX-OR Gate Realization

#### Using NOR gate

For the EX-OR gate realization, we require 5 NOR gates, as shown in the circuit diagram:

### EX-NOR Gate Realization

#### Using NOR Gate

For the EX-NOR gate realization, we require 4 NOR gates, as shown in the circuit diagram:

### NOR Gate Realization Using NAND Gate

For the NOR gate realization using the NAND gate, we require 4 NAND gates, as shown in the circuit diagram:

Shortcuts for the realization of logic gates are as follows:

 GATES Number of NOR gate NOT 1 AND 3 OR 2 EX-OR 5 EX-NOR 4

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