3. Logic gates and logic circuits
Chapter Overview
- Different types of Logic Gate
- NOT
- OR
- NOR
- XOR (EOR)
- AND
- NAND
- Pastpaper Question
3.1 Different types of Logic Gate
NOT GATE
An Inverter that only has one input, it reverses the logic state
Truth Table
| A | A‘ |
|---|---|
| 0 | 1 |
| 1 | 0 |
OR GATE
An OR gate can have two or more inputs. The output will be True if at least one input is true.
Truth Table
| A | B | A + B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
NOR GATE — An Universal logic gate
The reverse logic of OR gate
Truth Table
| A | B | (A + B)’ |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
XOR(EOR) GATE
A circuit which will give a True output if either, but not both, of its two inputs, is True
Truth Table
| A | B | A ⊕ B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
AND GATE
The output will be True when both inputs are true
Truth Table
| A | B | A * B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
NAND GATE — An Universal logic gate
The reverse logic of AND GATE
Truth Table
| A | B | (A * B)’ |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
3.2 Practice Time
