Embedded C Program: Understanding Variables, Operators, and I/O Operations, Slides of Computer Science

Download Embedded C Program: Understanding Variables, Operators, and I/O Operations and more Slides Computer Science in PDF only on Docsity!

An Embedded C Program

An Embedded C Program the simplest

form

2

void main()

while (1) //do forever

void main()

printf(“begin measuring speed”);

while(1) //do forever

4

#include <mega16.h> // the LED 0 on PORTB will be on unsigned char led_status=0xFE; // Timer 1 overflow interrupt service routine interrupt [TIM1_OVF] void timer1_ovf_isr(void) { // Reinitialize Timer 1 value TCNT1H=0xF8; TCNT1L=0xFB; // Place your code here // move the LED led_status<<=1; led_status+=1; if (led_status==0xFF) led_status=0xFE; // turn on the LED PORTB=led_status; } // Declare your global variables here

// Continue on next slide

Example used in

Lab 1

5

void main(void) { // Declare your local variables here // Input/Output Ports initialization // Port B initialization // Func7=Out Func6=Out Func5=Out Func4=Out Func3=Out Func2=Out Func1=Out Func0=Out // State7=1 State6=1 State5=1 State4=1 State3=1 State2=1 State1=1 State0= PORTB=0xFE; // PORTB is port B driver register DDRB=0xFF; // Data Direction Control Register, 1: output; 0: input // other initializations as needed by your program, such as A/D converter // usually all required work for initialization done by CodeVision Wizard // ---------------

// Global enable interrupts #asm("sei") while (1) { // Place your code here }; }

Variable Types and Sizes

7

Type Size(Bits) Range

bit 1 0,

char 8 -128 to 127

unsigned char 8 0 to 255

int 16 -32768 to 32767

short int 16 -32768 to 32767

unsigned int 16 0 to 65535

signed int 16 -32768 to 32767

long int 32

unsigned long int 32

signed long int 32

float 32 +-1.175e-38 to +- 3.4e

double 32 +-1.175e-38 to +- 3.4e

Constants

8

Numerical Constants decimal 1234 binary 0b hexadecimal 0xff octal 0777

Character Constants character representation Equivalent Hex Value

TAB ‘\t’ ‘\x09’ LF (new line) ‘\n’ ‘\x0a’ CR ‘\r’ ‘\x0d’ Backspace ‘\b’ ‘\x08’ -- -- example printf(“c = %d\n”, c) // printf(“c = %d\n\r”, c) //

Bitwise Operations

10

Given an unsigned char y = 0xC operation result x = ~y x = 0x x = y <<3 x = 0x x = y>>4 x = 0x0C x = y&0x3F x = 0x x = y^1 x = 0xC x = y | 0x10 x = 0xD

other examples: unsigned char z z = PINA & 0x06; PORTB = PORTB | 0x60; PORTB = PORTB & 0xfe;

Logical Operators

11

Logical operator AND && OR ||

x =5 and y = (x && y) is true, because both are non-zero (x & y) is false, because 00000101 bitwise AND 00000010 equal to zero

(x || y) is true, because either value is non-zero (x | y) is true, b101 bitwise OR b010 is b111 (non-zero)

I/O operations

13

unsigned char i; // temporary variable

DDRA = 0x00; // set PORTA for input DDRB = 0xFF; // set PORTB for output PORTB = 0x00; // turn ON all LEDs initially

while(1){ // Read input from PORTA. // This port will be connected to the 8 switches i = PINA; // Send output to PORTB. // This port will be connected to the 8 LEDs PORTB = i; }

I/O operations

14

Turn on an LED connected to PB PORTB |= 0xF7; // b11110111; PORTB=0x00 initially; Must do the whole port

Turn on an LED connected to PB PORTB.3 = 0 ; // access the bit 3 of port B, turn on the LED

for (delay = 0; delay < 10000; delay++); // declare delay as int somewhere

PORTB.3 = 1; // turn off the LED

Division

16

Beware division:

• If second argument is integer, the result will be integer (rounded): 5 / 10  0 whereas 5 / 10.0  0.
• Division by 0 will cause a problem

Relational Operators

17

Relational Operators

Is Equal to == Is Not equal to != Less Than < Less Than or Equal to <= Greater than > Greater Than or equal to >= x = 3 and y = (x == y) FALSE (x != y) TRUE (x < y) TRUE (x<=y) TRUE (x>y) FALSE (x >= y) FALSE

Assignment Operators

19

x = y assign y to x x++ post-increment x ++x pre-increment x x-- post-decrement x --x pre-decrement x

x += y assign (x+y) to x x - = y assign (x-y) to x x = y assign (xy) to x x /= y assign (x/y) to x x %= y assign (x%y) to x

int x=5; int y; y = ++x; /* x == 6, y == 6 */

int x=5; int y; y = x++; /* x == 6, y == 5 */

Do While loop

20

do // mix up the numbers { // while waiting for button release. first ^= seed>>1; // Exclusive ORing in the moving seed second ^= seed>>2; third ^= seed>>3; seed++; // keep rolling over the seed pattern }

while(PINA.0 == 0); // while the button is pressed