Understanding the NOR Gate
The NOR gate is a universal logic gate that produces an output of 1 (TRUE) only when both inputs are 0 (FALSE). It is the complement of the OR gate. The name NOR stands for "NOT OR" because the output is the negation of the OR operation. NOR gates are called "universal gates" because any other logic gate can be constructed using only NOR gates.
Logic Gate Comparison
NOR Gate
Output is 1 only when both inputs are 0.
OR Gate
Output is 1 when at least one input is 1.
NAND Gate
Output is 0 only when both inputs are 1.
NOR Truth Table
The NOR gate truth table for two inputs A and B:
- A=0, B=0: NOR = 1 (both inputs are 0)
- A=0, B=1: NOR = 0 (at least one input is 1)
- A=1, B=0: NOR = 0 (at least one input is 1)
- A=1, B=1: NOR = 0 (at least one input is 1)
NOR as a Universal Gate
Any Boolean function can be implemented using only NOR gates:
- NOT(A): NOR(A, A) = NOT(A OR A) = NOT(A)
- OR(A, B): NOR(NOR(A, B), NOR(A, B))
- AND(A, B): NOR(NOR(A, A), NOR(B, B))
Applications
NOR gates are fundamental in digital electronics and computer architecture. They are used in memory circuits (SR latches), CPU design, programmable logic arrays, and various combinational and sequential circuits. The fact that NOR is a universal gate makes it particularly important in VLSI design and FPGA programming.