Author: M Abo Bakar Aslam
OR Gate
The OR gate produces a HIGH output when any input is HIGH. It performs logical addition in combinational logic circuits.
1. Properties
- Minimum two inputs
- Output is 1, if any input is 1
- Output is 0, only if all inputs are 0
2. Symbol - 2 Inputs OR Gate
3. Boolean Expression - 2 inputs OR Gate
Y = A + B
4. Truth Table - 2 Inputs OR Gate
Total Number of Rows = 2^(number of inputs) = 2^2 = 4
Total Numbers: 0, 1, 2, 3
| A | B | Y |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
5. OR Gate with 3 Inputs
Symbol
Boolean Expression
Y = A + B + C
Truth Table
Total Number of Rows = 2^(number of inputs) = 2^3 = 8
Total Numbers: 0, 1, 2, 3, 4, 5, 6, 7
| A | B | C | Y |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 |
6. OR Gate with 4 Inputs
Symbol
Boolean Expression
Y = A + B + C + D
Truth Table
Total Number of Rows = 2^(number of inputs) = 2^4 = 16
Total Numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
| A | B | C | D | Y |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 1 |
| 0 | 0 | 1 | 0 | 1 |
| 0 | 0 | 1 | 1 | 1 |
| 0 | 1 | 0 | 0 | 1 |
| 0 | 1 | 0 | 1 | 1 |
| 0 | 1 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 | 1 |
| 1 | 0 | 0 | 1 | 1 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 0 | 1 | 1 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 0 | 1 | 1 |
| 1 | 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
7. OR Gate with 1 Inputs
This logic-gates actually doesn't exist but we can construct it by using 2-Input-OR-Gate.
Symbol
Boolean Expression
Y = A + A = A
Truth Table
Total Number of Rows = 2^(number of inputs) = 2^1 = 2
Total Numbers: 0, 1
| A | Y |
|---|---|
| 0 | 0 |
| 1 | 1 |