Standard Logic Gates
1. The 6 Standard Logic Gates
Each gate has a specific logic rule and a corresponding truth table showing every possible input/output combination.
NOT Gate
Output is the inverse of the input.
| A | OUT |
|---|---|
| 0 | 1 |
| 1 | 0 |
AND Gate
Output is 1 only if BOTH inputs are 1.
| A | B | OUT |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
OR Gate
Output is 1 if AT LEAST ONE input is 1.
| A | B | OUT |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
NAND Gate (NOT AND)
Output is 0 only if BOTH inputs are 1.
| A | B | OUT |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOR Gate (NOT OR)
Output is 1 only if BOTH inputs are 0.
| A | B | OUT |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
XOR Gate (Exclusive OR)
Output is 1 if inputs are DIFFERENT.
| A | B | OUT |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
2. Logic Algebra Symbols
In exams, you may see logic represented as equations:
- AND: $A \cdot B$ or $A \text{ AND } B$
- OR: $A + B$ or $A \text{ OR } B$
- NOT: $\bar{A}$ or $\text{NOT } A$
⚠️ Exam Note: When drawing a logic circuit from an expression like $X = (\text{A AND B}) \text{ OR (NOT C)}$, always work from the inside of the brackets outwards.