Eet203 Lecture 2 - Introduction to c Programming

8/2/2019 Eet203 Lecture 2 - Introduction to c Programming

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EET203

MICROCONTROLLERSYSTEMS DESIGN

LECTURE 2: INTRODUCTION TO CPROGRAMMING


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PIC16 C Program Basics

Variables

Looping

Decisions

The purpose of an embedded program is

(i) read in data or control inputs,(ii) process the data

(iii) operate the outputs as required


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Variables

A variable name is a label attached to thememory location where the variable value isstored.

In C, the variable label is automatically assignedto the next available location

The variable name and type must be declared atthe start of the program block

Only alphanumeric characters (az, AZ, 09)and underscore, instead of space, can be used.


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Variables

x is variable

int x;x= 99;PORTD = x;


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Looping

to execute continuously until the processor isturned off or reset

the program generally jumps back at the end

to repeat the main control loop

implemented as a while loop

int x;while(1){

PORTD = x;x++;

}

While loop


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Decision Making

To illustrate basic decision making is tochange an output depending on the state of aninput

int x;PORTD=0x00;while(1){

x=RC0;

if(x==1) RD0=1;}

If statement for the decision making

The value is then tested in the ifstatement and the output set

accordingly.


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PIC16 C Data Operations

Variable typesFloating point numbersCharactersAssignment operators

A main function of any computer program is to carry outcalculations and other forms of data processing

Data structures are made up of different types of numericaland character variables, and a range of arithmetical andlogical operations are needed

Microcontroller programs do not generally need to processlarge volumes of data, but processing speed is oftenimportant


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Variable Types

Variable - to store the data values used in the program

Variable labels are attached to specific locations whenthey are declared at the beginning of the program

MCU can locate the data required by each operation inthe file registers


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Integers

the default type is an unsigned 8-bit number, giving arange of values of 0 255

Range of a number is determined by the number ofdifferent binary codes that can be represented


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Signed Integers

uses the most significant bit (MSB) as the signbit, so the range is accordingly reduced by half

MSB 0 represents a positive number, MSB 1

indicates a negative number

Therefore, the range for a 16-bit signed integeris 32767 to + 32767

The sign bit must be processed separately toget the right answer from a calculation


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Character Variable

represented by ASCII codes

The basic set of 7- bit characters includes theupper and lower case letters and the numerals

and punctuation marks found on the standardcomputer keyboard


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Character Variable

The statement answer = 'Y ' ; will assign the value 0

x 59 to the variable answer

For example, capital(upper case) A is1000001 (6510 )


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Assignment Operations

A range of arithmetic and logic operations areneeded where single or paired operands areprocessed

The result is assigned to one of the operandvariables or a third variable


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Conditional Operations

Where a logical condition is tested in a while,if, or for statement, relational operators areused

One variable is compared with a set value oranother variable, and the block is executed ifthe condition is true Examples :

AND condition:if((a > b)& & ( c = d ))

OR condition:if((a > b)||(c = d ))


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PIC16 C Sequence Control

While loops

Break, continue, goto

If, else, switch


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While Loops

while(condition) : provides a logical test at thestart of a loop, and the statement block isexecuted only if the condition is true

do..while(condition) : the loop block beexecuted at least once, particularly if the testcondition is affected within the loop


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While Loops

The WHILE test occurs before the block and the DOWHILE after


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Break, Continue, and Goto

break the execution of a loop orblock in the middle of itssequence

The block must be exited in anorderly way, and it is useful tohave the option of restarting theblock (continue) or proceeding

to the next one (break). It is achieved by assigning a

label to the jump destination andexecuting a goto..label


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If..Else and Switch..Case

if-allows a block to be executed or skippedconditionally.

else- allows an alternate sequence to be

executed, when the if block is skipped


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If..Else and Switch..Case

multichoice selection -which is provided by theswitch..case syntax

switch..case : tests avariable value andprovides a set ofalternative sequences,one of which is selecteddepending on the testresult


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Array

List of variables that are all of the same type andcan be referenced through the same name

The individual variable in the array is called anarray element

Used to handle groups of related data Declaration for one-dimensional array

type var_name [size]

type valid C data type (char, int, long)

var-name the array name size specifies how many elements are in the array

Example: int height[50]; The first element to be at an index of 0 (height[0])

The last element to be at an index size-1(height[49])


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Array

Can also being declare as multidimensionalarray

Unsigned int height[4][5] 2 dimensional array

4x5 (4 rows, 5 columns) Assigning initial value

Int height[3] = { 23,45,67};

Int height[] = {23,45,67};Char str[3] = {a,b,c};

Char name[6] = Ernie; equal to char name[6]= {E,r,n,i,e,/0};

/0 is a null terminator indicates the end of string


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Pointer

A memory location (variable) that holds the address ofanother memory location

Declarationtype *var-name;

Type valid C data types Var-name name of the pointer

* - indicates that the variable is a pointer variable

Examplevoid main(void)

{

int *x;

int height[4] = {1,2,3,4};

a = &height; // assigned a to the first address of array (a) = height[0]

a++; // set the pointer a to next array address (a) = height[1]

printf(%d,*a); // print the array value as pointed by pointer a result is 2

}

Suitable for accessing look-up table

() means value of

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Eet203 Lecture 2 - Introduction to c Programming