1. PICS / Microcontrollers

2. Objectives Understand: What is a Microcontroller (µC)-PIC
What are the pros & cons of using µC’s
How to design using µC’s
Flowcharts
Basic pseudo code
Microcontrollers

3. What is a microcontroller (µC)
What is a microcontroller (µC)? PIC; Programmable integrated circuit is a microcontroller
The “process” element of any system it belongs to
Microcontrollers

4. What is a microcontroller ?
Essentially: a complete computer system on a chip !
CPU
Flash Memory (same as a USB memory stick)
Digital Inputs & outputs
Most (but not all) µC’s also have analog inputs
Need to be programmed to make them do something useful
Microcontrollers

5. Some Example µC Applications
Microcontrollers

6. microcontroller’s Lot of different types of PICs exist We use Genie
Stamp
Picaxe
OOPic
Arduino
We use Genie
Can be simulated & programmed whilst in circuit from a host computer via a USB cable from circuit wizard
Microcontrollers

7. Task
Generate 2 lists:
What inputs could potentially be connected to a microcontroller (PIC) ?
What outputs could potentially be connected to a microcontroller (PIC) ?
For each input & output, draw the symbol that is associated with it
Microcontrollers

8. Sample Task answer
Microcontrollers

9. µC Sizes PICAXE-18M GENIE-E18 PICAXE-14M GENIE-C14 PICAXE-08M
PICAXE-28X
GENIE-E28
Microcontrollers

10. Functionality A µC can be programmed to perform any logical function
Counting / maths
Sequencing
Latching
Delays / timing
Decoding
Encoding
Conditional switching
For simple functions, it may be more cost efficient to use dedicated hardware (counter chips / timer chips / logic gates)
Microcontrollers

11. Clocks
A microcontroller (PIC) executes one instruction every time it receives a clock pulse
TASKS: 1. Draw a clock waveform 2. Name a circuit that can produce a clock waveform?
Some simple microcontroller’s have internal clock generator circuits
Can also use crystals to generate very precise, very fast clocks
Microcontrollers

12. Microcontroller (PIC) Considerations
Cost
For simple functions, may be more expensive than simple logic
For complex functions may be more efficient
Speed
Typical clock speed for a Genie is 8MHz
May be slower than dedicated hardware
Complexity
The hardware is very simple
The complexity of design is in the programming (firmware)
Flexibility
microcontroller’s can be changed very easily during production or in the field (maintenance & reuse)
Size
Much more space efficient than dedicated logic or PC’s for complex functions
Power supply
They require a very precise voltage between 3.3 and 5.0 Volts
Microcontrollers

13. Review What is a microcontroller (PIC) µC ?
Do microcontroller’s do anything useful without being programmed ?
What could they be used for ?
Does changing the circuit function require a change to the electronic hardware ?
Does removing the power mean that the microcontroller needs reprogramming ?
What are some of the advantages of microcontroller’s
What are some of the disadvantages of microcontroller’s
Microcontrollers

14. How are microcontroller’s (PIC)Programmed ?
A program is developed & simulated on a PC
downloaded to the PIC via a programming cable
The program can be written directly using a programming language
BASIC C
Other
The program can be translated from a flow diagram
Microcontrollers

15. Review
How many times do you need to connect the microcontroller to a PC ?
How is the program developed on the PC ?
How do you know if the program you have written is going to do the right thing before you download it ?
Microcontrollers

16. Flowcharts - symbols Terminator: used to start or stop a program
Process box
Describes an action of some sort
The action may or may not be dependant on inputs
The action may not affect any outputs
Only one arrow may enter or leave the box
Decision box
Different routes out of the box can be taken
depending upon a condition
One arrow enters the box and two leave the box
- arrows leaving the box should be labelled
Set outputs
1 or more system outputs may change state
Only one arrow may enter or leave the box
Data flow direction arrows
Microcontrollers

17. Flowchart Example Specification:
start
Specification:
Turn on the lights as soon as it goes dark
Turn all lights off
Is it dark ? no
yes
Turn all lights on
Microcontrollers

18. Flowchart Task You have 5 minutes !! A quiz game for 2 players
Each player has a switch to activate a buzzer
You must decide which was pressed first and indicate your result by lighting one of two LED’s for 5 seconds
start
You have 5 minutes !!
Microcontrollers

19. start Turn off both LED’s Switch 1 pressed ? no yes Turn on LED 1 no
Wait 5s
Turn on LED 2
Wait 5s
Microcontrollers

20. Task
Show the sequence of events needed in the design of a pedestrian crossing
A switch gets pressed and the man goes from red to green
What else ????
You have 5 minutes !!
Microcontrollers

21. Traffic light = yellow (flashing)
start
Task Answer
Traffic light = green
“man” = red
Switch pressed ?
Traffic light = yellow
“man” = red
yes no
Wait 2s
Traffic light = red
“man” = green
Wait 20s
Traffic light = yellow (flashing)
“man” = red
Wait 2s
Microcontrollers

22. Exam Questions
For the past 3 years, at least one big question has been on Microcontroller (µC)-PIC
questions can be worth up to 22 marks
This is 2 full grades worth of marks !
Don’t worry about types of Microcontroller (µC)-PIC or exact programming code
Think about the logical processing flow that has to happen to make a function work
Microcontrollers