# NAND, NOR, EX-OR and EX-NOR Gate

The concept of NAND gate, NOR gate, Universal gate, Boolean functions, logic circuits or networks are explained briefly. These concepts are very important to grasp theme and theory of advance computer courses offered by several universities.

NAND, NOR, EX-OR, EX-NOR gate:

(a) NAND Gate: The NAND gate has two or more inputs signals but only one output signals. All input signals must be high to get a low output.

Truth table:

 A B (A.B)’ 0 0 1 0 1 1 1 0 1 1 1 0 NAND Gate

If the output of an AND gate is connected to the input of a NOT gate, the NAND circuit is formed.

(b) NOR Gate: The NOR gate has two or more input signals but only one output signals. All input must be low to get a high output. If the output of OR gate is connected to the input of a NOT gate, NOR gate is formed.

Truth Table:

 A B (A+B)’ 0 0 1 0 1 0 1 0 0 1 1 0 NOR Gate

(c) X-OR (Exclusive-OR) Gate: It is also called Not-Equivalent (NEQ) gate. This gate gives a 1 if A is 1 or B is 1, but not if both are 1.

Truth Table:

 A B XOR 0 0 0 0 1 1 1 0 1 1 1 0 X-OR Gate

(d) X-NOR or EQU (Equivalent) Gate: Logically equivalent to an XOR gate followed by an inverter. The truth table of X-NOR gate is the complement of an XOR truth table.  The output is the high when the inputs are same. X-NOR Gate

Truth table:

 A B EQU 0 0 1 0 1 0 1 0 0 1 1 1

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