Basic Logic Gate

Digital system is constructed by using logic gates. These gates are AND, OR, NOT,NAND, NOR,  XOR gates. The basic operation below are described and aid with truth table.

AND gate

The AND gate is an electronic circuit that give a output (1) only if it have all its inputs are 1. A dot (.) is used to show AND operation i.e A.B or sometimes written as AB.
The Boolean expression for AND operation is

                                X = AŸB

OR gate

 The OR gate is an electronic circuit that give output (1) if one or more of its input is 1. A plus (+) is used to show this operation.The Boolean expression for the OR operation is

X = A + B

Not gate

The NOT gate is an electronic circuit that produces an inverted version of the input as its output. It also known as an inverter. If the input variable is A, the inverted output is A’.

NAND gate

The NAND gate is combination of NOT-AND which is equal to an AND gate followed by a NOT gate. The output of all NAND gate are 1 if any of the inputs are 0.
The Boolean expression for the output of a 2-input NAND gate is

                                X = (AŸB)’

NOR gate

The NOR gate is the combination of NOT-OR which is equal to an OR gate followed by a NOT gate. The output of NOR gate are 0 if any inputs are 1.
The Boolean expression for the output of 2-input NOR gate is

                                X = (A+B)’

 XOR gate

The Exclusive-OR gate is a circuit which will give output 1 if either, but not both, of its two inputs are 1. An circled plus sign () is used to show the XOR operation.
The Boolean expression for XOR gate is

X=AŸB’+A’ŸB

   =AÅB