4.Microcontrollers

EN2852 – Applied Electronics4. Microcontrollers

By: Dr. S. ThayaparanBy: Dr. S. Thayaparan

Slide contents are extracted from the following source of origin :

1. http://en.wikipedia.org/wiki/Microcontroller

2. http://www.engr.sjsu.edu/bjfurman/courses/ME106/ME106pdf/MicroC_overview.pdf

3. http://www.mikroe.com/eng/chapters/view/64/chapter-1-introduction-to-microcontrollers/

4. http://www.mstracey.btinternet.co.uk/pictutorial/picmain.htm

5. http://www.codeproject.com/Articles/29528/Programming-the-PIC-Microcontroller-in-C-using-PIC

6. http://www.mikroe.com/eng/chapters/view/4/chapter-3-i-o-ports/

7. http://www.mikroe.com/eng/chapters/view/2/chapter-1-pic16f887-microcontroller-device-overview/

Applied Electronics Course Content

1. Op Amps

2. Sensors & Transducers

3. Electronic Instrumentation Systems

4. Microcontrollers

� Lectures are: 1.5 Hrs/Week

� Evaluation is : 60% Exam

40% CA

2

4.0 Microcontrollers

1. Introduction to Microcontrollers

2. Components of A Microcontroller

3. Microcomputer Architecture

4. Binary and Hexadecimal Numbers

5. Basic DSP Operations

A PIC 18F8720 microcontroller

in an 80-pin TQFP package

3

5. Basic DSP Operations

6. Programming Microcontrollers

Intel P8051 microcontroller

4.1 Introduction to Microcontrollers

� A microcontroller (sometimes abbreviated µC, uC or MCU) is a small

computer on a single integrated circuit (IC) containing a processor core,

memory, and programmable input/output peripherals

� Microcontrollers are used in automatically controlled products and

devices, such as automobile engine control systems, implantable medical

devices, remote controls, office machines, appliances, power tools, toys

and other embedded systems.

4

and other embedded systems.

� The first single-chip microprocessor was the 4-bit Intel 4004 released in

1971

� Even though there is a large number of different types of microcontrollers

and even more programs created for their use only, all of them have many

things in common.

� If you learn to handle one of them you will be able to handle them all.


� A typical scenario on the basis of which it all functions is as follows:

1. Power supply is turned off and everything is still…the program is loaded

into the microcontroller, nothing indicates what is about to come…

2. Power supply is turned on and everything starts to happen at high speed.

The control logic unit keeps everything under control. It disables all

other circuits except quartz crystal to operate. While the preparations

are in progress, the first milliseconds go by.

3. Power supply voltage reaches its maximum and oscillator frequency

5

3. Power supply voltage reaches its maximum and oscillator frequency

becomes stable. Special Function Registers (SFR) are being filled with bits

reflecting the state of all circuits within the microcontroller. All pins are

configured as inputs. The overall electronics starts operation in rhythm

with pulse sequence. From now on the time is measured in µS or nS.

4. Program Counter is set to zero. Instruction from that address is sent to

instruction decoder which recognizes it, after which it is executed with

immediate effect.

5. The value of the Program Counter is incremented by 1 and the whole

process is repeated...several million times per second.


6


7

4.1 Introduction to MicrocontrollersPIC16F887 Block Diagram

8


Read Only Memory (ROM)

• ROM is a type of memory used to permanently save the program.

• ROM size depends on the size of the program.

• ROM can be built in the microcontroller or added as an external chip.

• If ROM is external, the microcontroller is cheaper and the program can be

considerably longer.

• The internal ROM is usually smaller and more expensive, but leaves more

pins available for connecting to peripheral environment.

9

pins available for connecting to peripheral environment.

• The typical size of ROM ranges from 512B to 64KB.

Random Access Memory (RAM)

• RAM is used for temporary storing data and intermediate results created

and used during the operation of the microcontrollers.

• The content of this memory is cleared once the power supply is off.

• For example, if the program performs an addition, it is necessary to have a

register standing for the “sum”.

• The typical size of RAM goes up to a few KBs.

Electrically Erasable Programmable ROM (EEPROM)

• The EEPROM is a special type of memory not contained in all

microcontrollers.

• Its contents may be changed during program execution (similar to RAM ),

but remains permanently saved even after the loss of power (similar to

ROM).

• It is often used to store values, created and used during operation (such as


10

• It is often used to store values, created and used during operation (such as

calibration values, codes, values to count up to etc.), which must be saved

after turning the power supply off.

• A disadvantage of this memory is that the process of programming is

relatively slow and it is measured in miliseconds.

4.2 Components of A Microcontroller

11

4.3 Microcomputer Architecture

12

4.3 Microcomputer Architecturei8051 microarchitecture

13

� Microcontrollers are fundamentally digital and use binarylogic

� Digital : Two states: high and low, 1 or 0, on or off

• Often 5V or 0V

� One binary digitis called a bit

� It can take on two possible states: 1or 0

� Four binary digits is called a nibble

4.4 Binary and Hexadecimal Numbers

14

� Four binary digits is called a nibble

� Eight binary digits is called a byte


15


16


17

4.5 Basic DSP Operations

DSP : Digital Signal Processing

• Everything that we do in analog domain can be done in digital domain

Example 1: Signal Amplification

Example 2: Filtering (Low pass, band pass, high pass)

• Some things very difficult to do in analog domain can be easily done in digital

domain

Example 1: Finding the average value

18

Example 1: Finding the average value

Example 2: Finding the maximum value

• DSP has a very wide scope. We will only have a very brief look

• In digital domain, we work with fixed point numbers and variables

• Each variable/value is represented by a fixed number of bits

Example 1: Interger – 8 bits (signed & unsigned)

Example 2: Long Integer – 16 bits (signed & unsigned)

Example 3: Float – 32 or 64 bits (signed)

• In micro controllers, floating point variables are not common. We usually

have to use integers

4.5 Basic DSP Operations

• In simple micro-controllers, numbers are 8 bit values.

• How we interpret the numbers is up to us.

Example 1: 1111 1111 = 255 (unsigned interpretation)

Example 2: 1111 1111 = -128 (signed interpretation)

Example 3: 1000 0000 = 128

Example 4: 1000 0000 = 0.5

• We can also use two 8-bit variables to create 16-bit variable in our program

• It is important to keep the same interpretation throughout our algorithm

19

• It is important to keep the same interpretation throughout our algorithm

• Addition, substraction and multiplication

Example 1: after each adc operation do {

new_sig = sig_adc1 + sig_adc2;

}


new_sig = sig_adc1 - sig_adc2;

}


new_sig = sig_adc1 * 2;

}

4.6 Programming Microcontrollers

Example: 1 (For a pic micro-controller)

Operation : Smoothing (Low Pass Filtering)

function (adc_complete) {

val0 = 0;

val1 = 0;

sum = 0;

20

sum = sum + val0 + val1;

new_val = sum/3;

val0 = val1;

val1 = new_adc;

}

Example: 2 (For a pic micro-controller)

Operation : High Pass Filtering

- Substract the original with the LPF component.

Example: 2

int ledPin = 13; // LED connected to digital pin 13

void setup()

{

pinMode(ledPin, OUTPUT); // sets the digital pin as output

}


21

}

void loop()

{

digitalWrite(ledPin, HIGH); // sets the LED on

delay(1000); // waits for a second

digitalWrite(ledPin, LOW); // sets the LED off

delay(1000); // waits for a second

}


RA0-4 & RB0-7 : RA & RB are

bidirectional ports. Can be

configured as an input or an

output.

The number following RA is the

bit number (0 to 4). Each bit can

be configured as Input or Output.

VDD & VSS - Power supply pins

22

Pin-outs of the PIC 16F84

VDD & VSS - Power supply pins

VDD (+5V), VSS (0V)

OSC1/CLKIN & OSC2/CLKOUT

The microcontroller has some

kind of timing.

T0CK1: This is another clock

input, which operates an internal

timer. It operates in isolation to

the main clock.

MCLR - Used to erase the memory locations

inside the PIC (i.e. When re-program it). In

normal use it is connected to VDD.

INT - an input pin can be monitored. If it goes

high, we can do restart, stop or any other

function.

#include <htc.h>

#include <pic.h>

#include <delay.c>

main()

{

TRISB=0; // declare portb as output

for(;;) // do forever


TRISB = %00000000 -> set all PORTB pins as output

TRISB = %11111111 -> set all PORTB pins as input

PORTB = %11111111 -> make all PORTB pins high

PORTB.0[i] = 1 -> make pin number i high

23

for(;;) // do forever

{

RB0=1; // LED ON

DelayMs(250); // delay for 0.25 seconds

RB0=0; // LED OFF

Delayms(250);

}

} Note: A. PORTB : I/O port name

B. TRISA, TRISB: data-direction register name

C. These names are common to most PIC micros.

D. When power up, all the I/O pins are configured as inputs.


24


25

Port A and TRISA Register

ANSEL register :

• determine whether the pins will act as analog inputs or digital inputs/outputs.

RA0 = AN0 (determined by bit ANS0 of the ANSEL register);




1. #include <htc.h>

2. #include <pic.h>

3. #include <delay.c>

4. int j; // general global variables

5. void Wait_These_Seconds(float s) { // only to 3 decimals

6. int milli_Equiv; // milli second equivalent integer

7. milli_Equiv=1000*s;

8. for(j=1; j<=milli_Equiv; j++) { DelayMs(1); }

9. }

10. main() {

11. TRISB=0xF0; // RB4:RB7 are input ; 11110000 in binary

12. for(;;) {

13. if(RB7==1) {

14. RB0=1; // LED ON


26

14. RB0=1; // LED ON

15. Wait_These_Seconds(1.8); // delay for 1.8 seconds

16. RB0=0; // LED OFF

17. Wait_These_Seconds(0.9);

18. }

19. if(RB7==0) { // interrupt is connecting RB7 to ground

20. RB0=1; // LED ON

21. Wait_These_Seconds(0.7); // delay for 0.7 seconds

22. RB0=0; // LED OFF

23. Wait_These_Seconds(0.1);

24. }

25. }

26. }

Documents

4.Microcontrollers