Boolean Logic Diagrams (OCR GCSE Computer Science): Revision Notes

Boolean Logic Diagrams

Logic Gates Overview

• Logic gates are the basic building blocks of digital circuits. Each gate represents a different type of operation on binary input values (1 and 0).

AND Gate (Conjunction)

• Logic Symbol:
• Operation: Outputs 1 only when both inputs are 1. Otherwise, the output is 0.

Truth Table

A	B	A AND B
0	0	0
0	1	0
1	0	0
1	1	1

OR Gate (Disjunction)

• Logic Symbol:
• Operation: Outputs 1 if either or both inputs are 1. If both inputs are 0, the output is 0.

Truth Table

A	B	A OR B
0	0	0
0	1	1
1	0	1
1	1	1

NOT Gate (Negation)

• Logic Symbol:
• Operation: Outputs the inverse of the input. If the input is 1, the output is 0; if the input is 0, the output is 1.

Truth Table

A	NOT A
0	1
1	0

Combining Boolean Operators

When combining logic gates, more complex operations can be represented by combining multiple gates into circuits. For example:

A AND B OR NOT A

A	B	A AND B	NOT A	(A AND B) OR NOT A
0	0	0	1	1
0	1	0	1	1
1	0	0	0	0
1	1	1	0	1

Logic Gate Problem Solving

• Understanding the Truth Tables: The truth tables are used to evaluate the output for every combination of inputs. They help in designing and solving logic circuits.

• Problem Example: Given a circuit with multiple gates, use the truth table to find the output for each input combination.