1. ASCII
LP1

2. Binary Recap
You should now understand that your computer only uses binary code.
So how is it that we can press keys on a keyboard and the letter we pressed appears on the screen?
Does this mean that computers can understand the English alphabet?

3. Scenario
You’re sitting at your computer and you lean towards your keyboard.
You place your fingers on the keys and press one key:

4. Scenario
The keyboard is set up in such a way that each key press has a unique binary pattern to it.
In the case of the letter ‘A’ key this is
The letter ‘B’ key may is :
Each letter and symbol have their own unique binary code!

5. Scenario
Depending on the application you have open, the computer will decode this binary number to perform a specific task.
If you have Microsoft Word open, the application will insert the letter A on the document.
However, other software might simply respond to the key press by causing something to happen on the screen; for example many games use A as the “Move Left” key.
A = Move Mario Left

6. Character Set
A character set is the characters which are recognised/can be represented by the computer system.
The letter A has the binary value , which is equivalent to the denary value 65.
The key B has the binary value of , which is 66 in denary.
The key C has the binary value of , which is 67 in denary.
In fact, each key has a code based upon a standard called the American Standard Code for Information Interchange, or ASCII for short.

7. ASCII Here is the ASCII conversion table.
Notice that the ASCII character set can support lower case and upper case characters and also function keys like has space.

8. Activity
Using the ASCII character set, encode your first name and surname in binary:
Bruce Wayne
B r u c e
W a y n e

9. ASCII - Limitations
Since the ASCII character set requires 127 characters, it requires at least a 7 bit computer system to work.
27 = 2x2x2x2x2x2x2 = 128
What if you would like to use more characters in a computer system?

10. Unicode – 16 bit character set
Representing the character sets for several different language structures is not possible in ASCII, there are just not enough available characters that can be stored in a 7 bit system.
Unicode is a character set that was created to overcome this issue.
Unicode uses 16 bits to represent each character. This means that Unicode is capable of representing 65,536 different characters (216) and a much wider range of characters.

11. Questions
ASCII is a 7-bit character set. Calculate the total number of unique letters and symbols ASCII can support.
“ASCII Extended” is an 8 bit character set introduced a few years after ASCII. Calculate the total number of unique letters and symbols ASCII Extended can support.
Unicode is a 16-bit character set. Explain one advantage and one disadvantage of having using a character set that uses more bits per character.

12. Questions

13. Exam Questions

14. Extension Activity - Python
Create a program using Python that can convert the letters “a” to “z” into their 7bit ASCII binary digits.
If the user inputs in an “a”, the program will output
Extension:
Use a for loop to iterate through each letter in a string and each letter into 7bit binary.