Logic Gates
- A logic gate is a building block of a digital circuit. Logic gates perform a logical operation on one or more binary inputs to produce a binary output
- An electrical signal entering the logic gate is represented by a 1
- No electrical signal is represented by a 0
- There are several types of logic gates, each performing a specific logical operation
- Logic gates can be combined to carry out meaningful functions such as performing calculations or checking if data meets certain conditions
A table showing the symbol used to represent each logic gate
|
|
|
|
|
NOT |
|
The NOT gate takes a single binary input and outputs the opposite of the input |
|
AND |
|
The AND gate takes two inputs and produces one output Only two positive inputs (1 and 1) will result in a positive output of 1 If either of the inputs is a 0 the output will be a 0 |
|
OR |
|
The OR gate takes two inputs and produces one output If either of the inputs is positive (1) the output will be 1 |
|
NAND |
|
A NAND gate is a combination of an AND gate followed by a NOT gate. If both inputs are a 1 it will output a 0. Any other combination of inputs will result in an output of 1 |
|
NOR |
|
A NOR gate is a combination of an OR gate followed by a NOT gate. If both inputs are 0 it will output a 1. Any other combination of inputs will result in an output of 0 |
|
XOR |
|
An XOR gate (exclusive OR) will output a 1 if the inputs are different to one another (a 1 and a 0) |
Exam Tip
- You will need to either draw a diagram of a logic circuit using these symbols, or you will have to interpret an existing diagram. This is why it is important to remember the symbol of each gate and the logic rules for each one
