1. PYTHON PROGRAMING
Week 15 – Tuesday

2. have a go
Convert these denary numbers to binary: 23, 45, 62, 8, 14 Now convert them to hexadecimal Convert these hexadecimal numbers to binary: 3D, 1A, FF, 0F, 56 Now convert them to denary Work out these in binary: * * 62

3. last week Bitwise operators Binary addition Binary multiplication
Hexadecimal (base 16)
Denary to hex
Hex to denary

4. today
Targets!!
Representing negative numbers in binary (Two’s complement)
Binary subtraction
Representing fixed point fractional numbers in binary
File handling in Python

5. setting targets – comp1 & comp2
academic?
maths?
english?

6. twos complement Have you watched the videos?
Representation of negative numbers
Most significant bit holds sign
0 – positive
1 - negative
Flip the bits
Add 1
Negative 1 will always be all 1s in twos complement
Smallest negative number will always be a leading 1 followed by zeroes
Largest positive number will always be a leading zero followed by ones

7. binary addition– twos complement
How do you think we do this?

8. binary subtraction – twos complement
How do you think we do this?
What is the advantage of this when it comes to designing computer architecture?
NB Overflow
adding two positives giving a negative number (eg 3 bit system 3 + 2)
adding two negatives giving a positive number (eg 3 bit system -4 -7)

9. fixed point fractions in binary
What is fixed point
How do we represent the fractional part? ….
How can we represent other fractions eg .75, .375 …

10. exercises Text book page 107 Questions 6-9 page 108 Questions 10-11
plus any of the activites

11. Python - file handling Codecademy
Where are you?
What is your target for this week?
Try the file handling exercises on the web site
Do I need to go through file handling programs?
Smaller group?
NB example programs and notes are also on the site

12. PLENARY
How do we represent a negative number in binary? How many values can we represent in 4 bits? How many values can we represent in 8 bits? What is the largest positive number we can hold in a four bit signed system? What is the smallest negative number in a four bit signed system? What is the process for twos complement? How do we do binary subtraction? What is a fixed point number? How do we represent a fixed point number in binary? How did we get on with file handling?

13. tomorrow Revision for mock exam Exam questions
Binary, hex, twos complement …
Algorithm design tools
Creating programs from designs

14. homework
Have a look at revision topics and bring any questions tomorrow