NOR Gate

The NOR gate is also a universal gate. So, we can also form all the basic gates using the NOR gate. The NOR gate is the combination of the NOT-OR gate. The output state of the NOR gate will be high only when all of the inputs are low. Simply, this gate returns the complement result of the OR gate.

The logical or Boolean expression for the NOR gate is the complement of logical multiplication of inputs denoted by the plus sign as

(A+B)'=Y

The value of Y will be true when all of its inputs are set to 0.

Types of Digital Logic NOR Gate

The NOR gate is also classified into three types based on the input it takes. These are the following types of NOR gate:

The 2-input NOR gate

Just like other gates, it is also a simple form of the NOR gate. In this type of NOR gate, there are only two input values and an output value. There are 2²=4 possible combinations of inputs. The truth table and logic design are given below:

Logic Design

Truth Table

The 3-input NOR gate

Unlike the 2-input N gate, the 3-input NOR gate has three inputs. The Boolean expression of the logic NOR gate is defined as the binary operation addition (+). The NOR gate can be cascaded together to form any number of individual inputs. There are 2³=8 possible combinations of inputs. The truth table and logic design are given below:

Logic Design

Truth Table

The Multi-input NOR Gate

Just like the NAND gate, we can also form the n-input NOR gate. If the number of inputs required is odd, any "unused" input can be held low by directly connecting it to the power supply using low "suitable" pull-up resistors. There is the following expression of the 4-input NOR gate:

Y=((A+B)+(C+D))'

In simple words, it is expressed as:

Y=A NOR B NOR C NOR D

Logic Design