LESSON 02 – LOGIC GATES (AND, OR & NOT)

LESSON NOTE

INTRO TO LOGIC GATES (AND, OR, NOT)

• Boolean logic is used in electronic circuits. Two inputs meet at a logic gate and one output leaves the gate.
  
  
• The inputs are on or off (or 1 or 0). The output is on or off.
  
  
• Symbols for each gate:

AND gate

OR gate

NOT gate (inverter)

• Example – Draw a diagram of two inputs entering an AND gate. One input is on and the other is off. Show the output.

• Letters are often used to denote inputs and outputs.
  
  
• Example - The diagram below can also be written algebraically like this: A or B = Q
  
  

• We can now create more advanced logic devices by combining more than one logic gate. Here are a few examples:

• Example 1: Create the diagram that represents the following equation: (A and B) or C = Q

• Example 2: Create the truth table for the above diagram.

A	B	C	Q
0	0	0	0
0	0	1	1
0	1	0	0
0	1	1	1
1	0	0	0
1	0	1	1
1	1	0	1
1	1	1	1

Note: To create a logic table for more advanced logic devices, we simply list all inputs (and outputs) and then consider the result for every possibility.

• Example 3: Create the diagram that represents the following equation: not(A or B) = Q

• Example 4: Create the logic table for the above diagram.

A	B	Q
0	0	1
0	1	0
1	0	0
1	1	0