# Logic Gates - Symbol, Boolean Algebra and Truth Table

### Symbol of the Logic Gate

For each gate, the input or inputs are on the left of the symbol. The output is on the right

### The Truth Tables

1. The function of a logic gates can be shown by using the Truth tables.
2. A truth table lists all possible input together with the corresponding output.

### AND gate

Symbol:

Boolean Expression:
$X=A•B$
Truth Table:
 Truth Table INPUT OUTPUT 0 0 0 0 1 0 1 0 0 1 1 1

Notes:
The output is HIGH (1) only if both the inputs are HIGH (1).

### OR gate

Symbol:

Boolean Expression:
$X=A+B$
Truth Table:
 Truth Table INPUT OUTPUT 0 0 0 0 1 1 1 0 1 1 1 1

Notes:
The output is HIGH (1) only if one or more inputs are HIGH (1).

### NOT gate

Symbol:

Boolean Expression:
$X= A ¯$
Truth Table:
 Truth Table INPUT OUTPUT 0 1 1 0

Notes:
The output is the opposite of the input.

### NAND gate

Symbol:

Boolean Expression:
$X= A•B ¯$
Truth Table:
 Truth Table INPUT OUTPUT 0 0 1 0 1 1 1 0 1 1 1 0

Notes:
The output is LOW (0) only if both the inputs are HIGH (1).

### NOR gate

Symbol:

Boolean Expression:
$X= A+B ¯$
Truth Table:
 Truth Table INPUT OUTPUT 0 0 1 0 1 0 1 0 0 1 1 0

Notes:
The output is HIGH (1) only if both the inputs are LOW (0).