Input Controls
Live Display
| A | B | Output (Y = (A + B)') |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
Current Observation
Set inputs A and B using the toggle switches and observe how the NOR gate processes the signals. The output becomes HIGH (1) only when both inputs are LOW (0).
Signal Flow Observation
Toggle the switches to observe the signal flow animation through the wires. Notice how the output turns LOW whenever any input signal reaches the NOR gate as HIGH.
Definition
A NOR (NOT-OR) gate is a fundamental digital logic gate that produces a HIGH (1) output only when both of its inputs are LOW (0). If any input is HIGH (1), the output is LOW (0).
Working Principle
The NOR gate performs logical addition followed by logical inversion. It calculates the OR result of its inputs and complements the output state.
- When both inputs A and B are LOW (0) → internal OR is 0 → output is inverted to HIGH (1).
- When either input A OR input B is HIGH (1) → internal OR is 1 → output is inverted to LOW (0).
Universal Gate Property
NOR gates are classified as Universal Logic Gates because any fundamental Boolean function (AND, OR, NOT, NAND, XOR) can be constructed using combinations of only NOR gates.
Truth Table Summary
The 2-input NOR gate has 4 input combinations. Three combinations produce a LOW output, and only one combination (A=0, B=0) produces a HIGH output.
Boolean Expression
Y = (A + B)' (also written as Y = A + B or Y = NOT(A OR B))
Industrial Applications
- Automatic Night Lamp: The lamp turns ON (1) only when no input daylight signal is active (both light sensors detected 0).
- Universal Logic Implementation: Enables building any complex digital circuit by cascading a single NOR gate IC type (e.g. 7402 Quad NOR).
- Cleanroom Contamination Control: Keeps ventilation and purification systems active (1) only when no smoke or dust sensors detect contaminants (0).
- Digital Memory Latches: Cross-coupled NOR gates form fundamental SR latches and flip-flops used for binary data storage.
- Zero-Detection Circuits: Used in microprocessors to generate a flag signal when all parallel input bits are zero.
Boolean Expression
Y = (A + B)'
The prime (') or overbar represents the NOT (inversion) operation applied to the result of the OR operation (A + B).
De Morgan's Theorem
By De Morgan's Law, the NOR operation is logically equivalent to an AND operation with inverted inputs:
(A + B)' = A' · B'
Boolean Properties of NOR
- Inverter (NOT): A NOR A = (A + A)' = A'
- Commutative Law: (A + B)' = (B + A)'
- Non-Associative: (A NOR B) NOR C ≠ A NOR (B NOR C)
- Double Inversion (OR): ((A + B)')' = A + B
Current Calculation
A = 0, B = 0 → Y = (0 + 0)' = 1
Automatic Night Lamp System
This demonstrates an automatic night lamp system using NOR gate logic. The night lamp turns ON (1) only when no input signal is active (0) — i.e., when both ambient light sensors detect darkness.
If either Sensor 1 OR Sensor 2 detects ambient daylight (1), the NOR gate output becomes LOW (0), automatically turning OFF the night lamp to save energy.