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POLITECNICO DI MILANO

www.polimi.it

Microcontrollers

INTRODUCTION and C Review

[email protected] 2 / 231 ELECTRONIC SYSTEMS’ lab - MICROCONTROLLERS 00

Outline

• Course introduction

• What is a µController and how it works

• Memory organization and Registers

• Instructions and Programming Languages

• Peripherals

• Development Tools

• Laboratory goals

• C language review


Course Introduction

• Main activities:• Learn the main microcontroller peripherals• Write code• Program and use a real device

• Agenda:From 16.30 to 16.45 From 16.45 to 18.00

19-22/10 Lesson 1 Introduction & C language SW and board overview

26-29/10 Lesson 2 Ports & Interrupts Hands-on

2-5/11 Lesson 3 Timers & 7-seg display Hands-on

9-12/11 Lesson 4 ADC & LCD Hands-on

16-19/11 Lesson 5 Capture Compare PWM Hands-on

23-26/11 Lesson 6 Code optimization with assembly Hands-on


Course Introduction

• Organizational stuff:

• Group A : Mondays, 16.30 – 18.00• Group B : Tuesdays, 16.30 - 18.00• Group C : Wednesdays, 16.30 – 18.00• Group D : Thursdays,16.30 – 18.00

• At least one PC per working-group (2-4 people)• A USB stick may be useful

• Contacts: [email protected]@[email protected]@polimi.it


What is a microcontroller

Flexible and cost effective devices Mainly used for embeddedapplications

Single integrated device, containing a processing core, program and data

memories and manyperipheral modules(also mixed-signal)

Wide range of devices:FROM 8-bit architecture, 4 MHz, in SOT23-6 package TO 32-bit architecture, 200 MHz, with ethernet and USB


How it works

• Harvard-based architecture• 35 instructions RISC processor core• Internal program and data memory• Multi-priority interrupt capability• Different kinds of peripheral modules and interfaces


Memory Organization (1)

PIC18F45K22 (used during this course):

• 21-bit program counter, capable of addressing up to

2 MB max program memory space

• Program Memory: 64 kB (EEPROM)

• Data Memory: 3896 kB of STATIC RAM

Data Memory is divided into:

• Special Function Registers, used by the CPU and peripherals for controlling the desired operation of the device

• General Purpose Registers, used for temporary data storage


Memory Organization (2)

There are three types of Special Function Registers (SFR):

• Core Registers:

Deal with CPU operation, interrupts control and input/output ports(W, STATUS, INTCON, TRISA…)

• Peripheral Registers:

Control the operation of peripheral modules: enable, settings and data input/output (ADCON, CCPR, SSPCON, TXSTA…)

• Configuration Registers:

Used for start-up configurations, oscillator settings, in-circuit programsettings and code protection purposes (CONFIG1, CONFIG2…)


Instructions and programming

ASSEMBLY:

• Hardware-level language• High complexity• Highest code optimization• Predictable timing

High-level Languages:

• C (industry standard), Pascal• Better code understanding

(natural language elements)• Code optimization managed by

the compiler (Low)• Higher portability of code


RISC Instruction Set

• RISC architecture: only 35 instructions

• Predictable Timing: each instructioncompletes in one(or two) cycles → possibility to create delay routines


Peripherals

PIC18F45K22 (used during this lessons):

Why a Microcontroller instead of a Microprocessor?

PERIPHERALS ARE THE REAL BENEFIT OF USING A MICROCONTROLLER

A µC can directly interface with external world

• GPIO with interrupt on change and internal pull-up• Multichannel 10-bit ADC with internal voltage reference• 16-bit Timer/Counter module• Capture/Compare/PWM module• Enhanced USART module• Master Synchronous Serial Port (MSSP)• Analog Comparator module


PIC18F45

HIGH PERFORMANCE RISC CPU FEATURES• Only 35 single word instructions to learn• Operating speed: DC - 20 MHz clock input• 1024 words of program memory• 4k bytes of Data RAM• 64k bytes of Data EEPROM• 16-bit wide instruction words• 8-bit wide data bytes

PERIPHERAL FEATURES• 35 I/O pins with individual directioncontrol• High current sink/source for direct LED drive- 25 mA sink max. per pin- 25 mA source max. per pin• TMR0: 8-bit timer/counter with 8-bitprogrammable prescaler

CMOS ENHANCED FLASH/EEPROM TECHNOLOGY

• Low power, high speed technology• Fully static design• Wide operating voltage range:- Commercial: 2.0V to 5.5V- Industrial: 2.0V to 5.5V• Low power consumption:- < 2 mA typical @ 5V, 4 MHz- 15 mA typical @ 2V, 32 kHz-< 0.5 mA typical standby current @ 2V

SPECIAL MCU FEATURES• In-Circuit Serial Programming™ (ICSP™)

• Power-on Reset, Power-up Timer,Oscillator Start-up Timer• Watchdog Timer with On-Chip RC oscillator


PIC18F45123

54

18

1617

1514

1213

11

6

87

109

RA0RA1

RA4

VSS

MCLR/Vpp

RA7/CLKIN

RA6/CLKOUT

VDD

PO

RTE

PO

RTA

PO

RTB

PO

RTD

OS

C

POWER-UP TIMERSTART-UP TIMER

POWER ON RESETWDT

PC

TIMER0

STACK

REG. FILE

W

ALU

EEPROMProgram

Mem

EEPROMData Mem

1920 21

22232425262728293031323334353637383940

VDDVSS

RA2

RA3

RA5

PORTD

ADC

EUSART

MSSP

RE0RE1RE2

PO

RTC

PO

RTC

RC0RC1RC2

RC3RD0RD1

RD3RD2

RC5RC4

RC7RC6

RD5RD4

RD7RD6

RB1RB0

RB3RB2

RB5RB4

RB7RB6


Architecture

Opcode is loaded from Program Memory to Instruction Register

A section of Opcode represents the data to transfer

The data to transfer isstored into Workingregister

The following instruction will load the content of Working register and store it into the destination register

How can I write a number in a register?


Architecture



The data to transfer is stored into Working register



Architecture






Architecture





So I need two separate instructions to do that!


Development Tools (1)

Programming IDE and compiler


Development Tools (2)

Microchip PicKit 3 Mikroelektronika EasyPIC v7

In-Circuit programmer/debugger Development Board


Course Goals

• Program a µC

• Handle Interrupts and manage timers

• Interface with peripherals (ADC, CCP …)

• Connect to external circuits (displays, real-time clock, …)

• Put all this stuff together in a complex project


Variables

They are used to reserve a determined memory area in order to store one or more numerical values, characters, strings…

They can be divided into several types: int (16 bit), long int (32 bit), short (8 bit), char (8 bit), float, double…

Each variable has to be declared in the function using it (unless it is a global variable) and they can be accessed only in the calling function.

They are identified by a mnemonic label chosen by the programmer.

EX:

void main()

{

int first;

Char second;

…

}


Global Variables

They are declared outside functions.

Their access is limited to the .c they are declared in (unless we use externalvariables).

EX:int b; Global variable declarationvoid function1(){

b = 10; Global variable used in a function…

}void function2(){

int c; Local variable declarationc = b + 1; Both types are used here…

}


Vectors

They are made by contiguous memory areas that can be accessed by a common mnemonic label and an index

char b[6];

b[3] = 1;


Pointers

It is a peculiar type of variable used to store a memory address pointing to another memory area containing data

int *p;

int b;

p = &b;

char b[6];

char *p;

p = b; (p = &(b[0]);)


Cast

It is used to transform a type of variable into another

int b;

char c;

b = 10;

c = (char) b;

• This way of working is called explicit cast because the programmerexpresses his intention of changing the type of a variable.

• Casts can also be implicit. This kind of cast operation is highly dangerouswhen a variable with a certain memory usage is transformed into a smaller variable.


Mathematical Operations

• +,-,*,/

• % (mod)

• =

• Other mathematical operators are implemented using specific librariesbut they require a significant computational time:

– log, exp, sin, cos, sqrt

• Sometimes we can use tricks to make the computational time shorter:

– For instance, multiplying a variable by 2 is equivalent to shift all its bits one position to the left, which is tremendously faster

a * 2 a << 2


Logical Operations

BITWISE OPERATIONS& -- bitwise and| -- bitwise or^ -- bitwise xor! -- bitwise not

COMPARISON OPERATIONS== -- equal!= -- different< -- smaller than> -- greater than<= -- smaller or equal>= -- greater or equal&& -- and|| -- or


If

if (condition)

{

//true branch

}

else

{

//else branch

}

EX: if ((a == 1) || ((b < 5) && (b > 1)))


Switch

switch (a)

{

case 1:

//code executed when a==1

break;

case 2:

//code executed when a==2

break;

default:

//code executed in all other cases

break;

}


Loops (1/2)

Loops are used to execute portions of code until a condition is met

While loop

While (condition)

{

//code

}

Do … While loop

do

{

//code

}

while(condition)


Loops (2/2)

For loop

for (initial assignments; condition; operation)

{

//code

}

for (int i = 10; i > 0; i --)

{

//this code is executed ten times

}


Functions

Prototype definition

Type function_name (type, type, …);

Function definition

Type function_name (type input1, type input2, …){

//code

}

Function call

Output = function_name (input1, input2, …);


Functions (example)

Prototype definition

int square (int);

Function definition

int square (int input){

int output = input * input;

return output;

}

Function call

int x = 5;

int y = square (x);


C for microcontrollesTo write in C language for µC is very similar to writing code for PCs.

DIFFERENCE: There are no standard I/O but physical I/O lines.

Printf( “numero = %d”, 8); PORTB=0b00001000;

Various C compilers have many common characteristics:

• ANSI C instruction set

• Supported data types (bit, char, int, long, double)

Differences are usually found in the syntax used to access hardwareresources of the microcontroller.

TRISB = 0x00;PORTB = 0x01;

set_tris_b(0x00);output_b(0x01);

HI-TECH PICC CCS PICC

Register settings Function call


DESIGN FLOW – C LANGUAGE

C code Assembler

HEX file

COF file

Programming

Simulationand debug

If bad firmware

Assemblycode

zsdzs

Documents

core registers

registers instructions

code program

eeprom data memory

group c

trisa peripheral registers

program counter

static ramdata memory