Logic Gates

• Computing
• Lower Secondary (Key Stage 3)

Logic Gates

KO: Demonstrate an understanding of logic gates and Boolean logic

All

• To be-able to recognise a logic gate.
• To be-able to understand the three different logic gates (NOT, AND, OR).

Most 

• To be-able to recognise the different logic gates and complete truth tables for them.
• To be-able to solve several gate problems. 

Some 

• To be-able to create a circuit using the different logic gates.
• To demonstrate an understanding of Boolean logic and Algebra

Starter

What could you see in the previous slide?

Main Activity

What is a Logic Gate?

A logic gate is a device that acts as a building block for digital circuits. They perform basic logical functions that are fundamental to digital circuit.

What is a 'Truth Table'?

This is a way of representing the inputs of the gates in a table using Boolean representation – 1’s & 0’s, or true & false. Each logic diagram has its own unique truth table.

What are the different Logic Gates?

AND, OR, XOR, NOT, NAND, NOR and XNOR.

The most common logic gates are:

AND Gate

NOT Gate 

OR Gate

Video 

Click here to watch 

AND Gate - Diagram and Truth Table

Output is true if: All inputs are true

NOT Gate - Diagram and Truth Table

Output is true if:​ Input is false​

Output is false if:​ Input is true

OR Gate-Diagram and Truth Table

Output is true if:​  At least one Inputs is true

Let's have a go at creating these...

Click on this link

I want you to create the AND, NOT, OR Gates.

More than one input...

AND Gate 

More than one input

OR Gate

Multiple Gates

Gates can be connected to other gates for more complex circuits​

Below we can see an AND gate along with a NOT gate. This is also in your worksheet

Multiple Gates

Below we can see an AND gate along with a OR gate.

What we have learnt so far...

• Truth tables represent what a binary output will be based on binary inputs and the currently used logic gate​.

• AND gates will produce a binary value of 1 when all inputs are a binary value of 1​.

• OR gates will produce a binary value of 1 when at least 1 input is a binary value of 1​.

• NOT gates will produce the opposite value of the input.

Boolean Algebra

What is 'Boolean Algebra'?

The text that describes the way the gates are connected.

Y = A AND NOT B

Y = NOT(A AND B)

Y = (A AND B) OR C

What would be the expression for this?

Research Task

In your small groups you must research the remainder of the gates. I want a definition and example.

XOR, NOR, XNOR, NAND

Be prepared to share with the class.

Plenary

OR

NOT

AND

What is the correct expression for the OR Gate

1. Y = A OR B
2. Y = A OR C
3. A OR B = Y
4. Y = A - B