The NOR Gate

• A NOR gate is a combination of OR gate and NOT gate. So we can say it is a NOT-OR operation. It may have two or more input and an output. The logical symbols and the truth table of NOR gate are,

• 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 1, A B = = then 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.
• The logical expression for the output is
• The NOR gate is also called active LOW AND gate.
• The switching circuit of a NOR gate is,

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

• NOR gate follows the commutative law as

Note: Unused input in any multi input NOR gate is always connected to the enable logic or Pull-Down.