4-4 logic gates

4.4 Logic Gates

4.4 Logic Gates

An electronics circuit with one or more inputs and a single output.Input and output can be either high (logic 1) or low (logic 0)

4.4 Logic Gates

Truth table is a table that summarises all the possible inputs and outputs of a logic gate.

4.4 Logic Gates

Boolean Algebra one form of expression which can be used to summarise the logic operation.

For example:

Logic gate NOR.

X =

The AND gate

0

0

Input Output / Q

A B

0 0 0

0

1 0 1 0

1

01 0 01 1 1

1

1

001

X = A. B

The OR gate

0

Input Output / Q

A B

0 0 0

0

0 1 1

1 0 11 1 1

0

X = A + B

The NOR / NOT- OR gate

1

Input Output / Q

A B

0 0 1

1

0 1 0

1 0 01 1 0

0

The NAND / NOT- AND gate

1

Input Output / Q

A B

0 0 11

0 1 1

1 0 11 1 0

0

Combination of logic gates

AND gate OR gate

Inputs

Logic operation Output

Inputs Logic operation

Output

A B C Q0 01 11 00 1

0

0

0 1

0 1

1

1

1 0

1 0

1

0

0

0

1

1

0

1

0

0 1

0 0 11

0 1 01

1 1 0 0

1100AND gate

0 1 0 0

0 0 11

0 1 01

1 1 0 0

1100

1 0

0 1

1010

1 0

0 0

Q

Q

Application of logic gate in control systems

Fire control system

Smoke detector

heat detector

A

B

Fire extinguisher

Fire alarm

Input Output

A B Fire extinguisher

Fire alarm

1 1

1 0

0 1

0 0