PICS / Microcontrollers

canolaokahumpkaElectronics - Devices

Nov 2, 2013 (4 years and 10 days ago)

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PICS / Microcontrollers

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

2

Microcontrollers

What is a microcontroller (µC)?

PIC; Programmable integrated circuit is a microcontroller


The “process” element of any system it belongs to

3

Microcontrollers

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


4

Microcontrollers

Some Example µC Applications

5

Microcontrollers

microcontroller’s


Lot of different types of PICs exist


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

6

Microcontrollers

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


7

Microcontrollers

Sample Task answer

8

Microcontrollers

µC Sizes

PICAXE
-
08M

GENIE
-
C08

PICAXE
-
14M

GENIE
-
C14

PICAXE
-
18M

GENIE
-
E18

9

Microcontrollers

PICAXE
-
28X

GENIE
-
E28

PICAXE
-
20M

GENIE
-
C20


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)


10

Microcontrollers

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

11

Microcontrollers

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



12

Microcontrollers

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



13

Microcontrollers

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

14

Microcontrollers

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 ?


15

Microcontrollers

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

16

Microcontrollers

Flowchart Example

start

Is it dark ?

yes

no

Specification:

Turn on the lights as soon as it
goes dark

Turn all
lights on

Turn all
lights off

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Microcontrollers

Flowchart Task


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 !!

18

Microcontrollers

start

Switch 1
pressed ?

yes

no

Switch 2
pressed ?

no

yes

Wait 5s

Wait 5s

Turn off
both
LED’s

Turn on
LED 1

Turn on
LED 2

19

Microcontrollers

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 !!

20

Microcontrollers

Task Answer

start

Traffic light = green

“man” = red

Switch
pressed ?

yes

no

Traffic light = yellow

“man” = red

Traffic light = red

“man” = green

Wait 20s

Traffic light = yellow (flashing)

“man” = red

Wait 2s

Wait 2s

21

Microcontrollers

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

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Microcontrollers