What is AND OR and NAND NOR functions?
These are Logical gates.
Logical gate:
Electronic device that can perform boolean function.
One or more logical inputs produce a single output.
Elementary building block of a digital circuit.
Digital circuit:
Signal must be one of two discrete levels.
Invention:
In 1924, Walther Bothe.
Also called as:
Universal logical gates.
How logic gates are made?
Transistors and diodes.
Transistor:
Regulates current or voltage flow.
Diode:
Two transmitting terminals allows current to flow only in one direction block current in opposite direction.
Why this logic gate is used?
To store data.
How many logical gates are there?
Seven logical gates.
What are they?
AND
OR
XOR
NOT
NAND
NOR
XNOR
AND gate:
A high output (1) results only if both the inputs to the AND gate are high (1).
Symbol:
Truth table:
XNOR
AND gate:
A high output (1) results only if both the inputs to the AND gate are high (1).
Symbol:
 |
| Representation of AND symbol |
| Input | Output | |
|---|---|---|
| A | B | Y=A.B |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
A high output (1) results if one or both the inputs to the gate are high (1).
Symbol:
Symbol:
 |
| Representation of OR symbol |
| Input | Output | |
|---|---|---|
| A | B | Y=A+B |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Output results (1) if one and only one of the inputs to the gate is true.
Symbol:
 |
| Representation of XOR symbol |
| Input | Output | |
|---|---|---|
| A | B | Y=A xor B |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOT gate has only one input signal.
Known as Inverter gate.
Symbol:
Truth table:
Truth table:
XNOR gate:
Advantages:
 |
| Representation of NOT symbol |
Truth table:
| Input | Output |
|---|---|
| 0 | 1 |
| 1 | 0 |
NAND gate:
NAND gate produces an output which is false only all inputs are true.
Symbol:
NAND gate produces an output which is false only all inputs are true.
Symbol:
 |
| Representation of NAND symbol |
| Input | Output | |
|---|---|---|
| A | B | Y=A nand B |
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOR gate:
A high input (1) results if both the inputs to the gate are low (0).
A high input (1) results if both the inputs to the gate are low (0).
If one or both input is high (1), a low output (0) results.
Symbol:
Symbol:
 |
| Representation of NOR symbol |
Truth table:
| Input | Output | |
|---|---|---|
| A | B | Y=A nor B |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
A high output (1) results if both the inputs to the gate are same.
If one but not both inputs are high (1), a low output (0) results.
Symbol:
Symbol:
 |
| Representation of XNOR symbol |
Truth table:
| Input | Output | |
|---|---|---|
| A | B | Y=A xnor B |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Less expensive.
Switching time is faster.
Disadvantages:
Uses more energy.
Electronic systems could not run.
Applications:
Oscillations for clock signals.
Mobile computers.
Digital watches.
Diodes or transistors as electronic switches.