PIC18F4550 HC-SR04 and PWM on Assembler

[Hector Otarola Garces]

Hey!

I'm working on a project, I'm using a PIC18F4550, I'm trying to measure distances with a HC-SR04 sensor, I have to trig a 10us pulse to the sensor, and I receive a pulse back from the echo. Wider the pulse, longer the distance. I'm trying to use interrupts to start counting with Timer0 the time that echo is '1'. The problem here, is that I can't measure the back pulse. I can't get into the interrupt succesfully and the timer doens't count what I need.

On the interrupt I write on PR2 register to change frecuency of PWM, but I haven't succeded yet. I already sent 10us pulses and I received an echo, but I haven't been able to use the timer properly.

I hope you can help me! 

Here's my code.

LIST P=18F4550

#include p18f4550.inc                ; Include register definition file

 

CONFIG WDT = OFF

CONFIG MCLRE = ON

CONFIG DEBUG = ON

CONFIG LVP = OFF

CONFIG FOSC = XT_XT

 

 

CBLOCK 0x080

   D1 ;variable usada para salvar contexto

   D2

ENDC

 

 

org 0x0000

 

goto Inicio

 

org 0x0008

 

goto INTERRUPCION

 

 ;Puertos

Inicio

CLRF    PORTB

movlw   b'00001111'

movwf   ADCON1

BSF TRISB,7 ; RB7 AS INPUT (ECHOIN)

BCF TRISA,0 ; RA0 AS OUTPUT (TRIGGER)

CLRF TRISC

movlw b'01000111'

movwf T0CON

 

;Interrupciones

bsf INTCON, GIE

bsf INTCON, RBIE

bcf INTCON, RBIF

 

; Configuracion PWM

 

MOVLW b'00000110'; BIT 2 Activar

MOVWF T2CON

MOVLW b'00011100'

MOVWF CCP1CON

MOVLW d'220'

MOVWF PR2

 

TRIGGER; CREADOR DE PULSO DE 10US

BSF PORTA,0

nop

nop

nop

nop

nop

nop

nop

nop

nop

BCF PORTA,0

CALL DELAY60MS; PARA NO CREAR PULSOS EN MENOS DE 50MS

goto TRIGGER

 

INTERRUPCION

bsf T1CON, TMR0ON

INTERRUPCION_2

btfsc PORTB,7

goto INTERRUPCION_2

bcf T1CON, TMR0ON

movwf TMR0L

movlw CCPR1L

bcf INTCON, RBIF

retfie

 

 

DELAY60MS

MOVLW D'223'

MOVWF D1

MOVLW D'65'

MOVWF D2

 

DELAY_1

DECFSZ D1

GOTO DELAY_1

DECFSZ D2

GOTO DELAY_1

RETURN

    

END

 

[Prabakaran P M]

#define _XTAL_FREQ 8000000



#define RS RD2

#define EN RD3

#define D4 RD4

#define D5 RD5

#define D6 RD6

#define D7 RD7



#include <xc.h>

#include "lcd.h";

#include <pic16f877a.h>



// BEGIN CONFIG

#pragma config FOSC = HS

#pragma config WDTE = OFF

#pragma config PWRTE = OFF

#pragma config BOREN = ON

#pragma config LVP = OFF

#pragma config CPD = OFF

#pragma config WRT = OFF

#pragma config CP = OFF

//END CONFIG



int a;



void interrupt echo()

{

if(RBIF == 1)                       //Makes sure that it is PORTB On-Change Interrupt

{

RBIE = 0;                         //Disable On-Change Interrupt

if(RB4 == 1)                      //If ECHO is HIGH

TMR1ON = 1;                       //Start Timer

if(RB4 == 0)                      //If ECHO is LOW

{

TMR1ON = 0;                     //Stop Timer

a = (TMR1L | (TMR1H<<)/58.82; //Calculate Distance

}

}

RBIF = 0;                           //Clear PORTB On-Change Interrupt flag

RBIE = 1;                           //Enable PORTB On-Change Interrupt

}

void main()

{

TRISB = 0b00010000;                 //RB4 as Input PIN (ECHO)

TRISD = 0x00;                       // LCD Pins as Output

GIE = 1;                            //Global Interrupt Enable

RBIF = 0;                           //Clear PORTB On-Change Interrupt Flag

RBIE = 1;                           //Enable PORTB On-Change Interrupt



Lcd_Init();



Lcd_Set_Cursor(1,1);

Lcd_Write_String("Developed By");

Lcd_Set_Cursor(2,1);

Lcd_Write_String("electroSome");



__delay_ms(3000);

Lcd_Clear();



T1CON = 0x10;                       //Initialize Timer Module



while(1)

{

TMR1H = 0;                        //Sets the Initial Value of Timer

TMR1L = 0;                        //Sets the Initial Value of Timer



RB0 = 1;                          //TRIGGER HIGH

__delay_us(10);                   //10uS Delay

RB0 = 0;                          //TRIGGER LOW



__delay_ms(100);                  //Waiting for ECHO

a = a + 1;                        //Error Correction Constant



if(a>=2 && a<=400)                //Check whether the result is valid or not

{

Lcd_Clear();

Lcd_Set_Cursor(1,1);

Lcd_Write_String("Distance = ");



Lcd_Set_Cursor(1,14);

Lcd_Write_Char(a%10 + 48);



a = a/10;

Lcd_Set_Cursor(1,13);

Lcd_Write_Char(a%10 + 48);



a = a/10;

Lcd_Set_Cursor(1,12);

Lcd_Write_Char(a%10 + 48);



Lcd_Set_Cursor(1,15);

Lcd_Write_String("cm");

}

else

{

Lcd_Clear();

Lcd_Set_Cursor(1,1);

Lcd_Write_String("Out of Range");

}

__delay_ms(400);

}

}

 

---

LCD.H

---

 

//LCD Functions Developed by electroSome

 

 

void Lcd_Port(char a)

{

if(a & 1)

D4 = 1;

else

D4 = 0;

 

if(a & 2)

D5 = 1;

else

D5 = 0;

 

if(a & 4)

D6 = 1;

else

D6 = 0;

 

if(a &

D7 = 1;

else

D7 = 0;

}

void Lcd_Cmd(char a)

{

RS = 0;             // => RS = 0

Lcd_Port(a);

EN  = 1;             // => E = 1

        __delay_ms(4);

        EN  = 0;             // => E = 0

}

 

Lcd_Clear()

{

Lcd_Cmd(0);

Lcd_Cmd(1);

}

 

void Lcd_Set_Cursor(char a, char b)

{

char temp,z,y;

if(a == 1)

{

 temp = 0x80 + b – 1;

z = temp>>4;

y = temp & 0x0F;

Lcd_Cmd(z);

Lcd_Cmd(y);

}

else if(a == 2)

{

temp = 0xC0 + b – 1;

z = temp>>4;

y = temp & 0x0F;

Lcd_Cmd(z);

Lcd_Cmd(y);

}

}

 

void Lcd_Init()

{

  Lcd_Port(0x00);

   __delay_ms(20);

  Lcd_Cmd(0x03);

__delay_ms(5);

  Lcd_Cmd(0x03);

__delay_ms(11);

  Lcd_Cmd(0x03);

  /////////////////////////////////////////////////////

  Lcd_Cmd(0x02);

  Lcd_Cmd(0x02);

  Lcd_Cmd(0x08);

  Lcd_Cmd(0x00);

  Lcd_Cmd(0x0C);

  Lcd_Cmd(0x00);

  Lcd_Cmd(0x06);

}

 

void Lcd_Write_Char(char a)

{

   char temp,y;

   temp = a&0x0F;

   y = a&0xF0;

   RS = 1;             // => RS = 1

   Lcd_Port(y>>4);             //Data transfer

   EN = 1;

   __delay_us(40);

   EN = 0;

   Lcd_Port(temp);

   EN = 1;

   __delay_us(40);

   EN = 0;

}

 

void Lcd_Write_String(char *a)

{

int i;

for(i=0;a!='';i++)

  Lcd_Write_Char(a);

}

 

void Lcd_Shift_Right()

{

Lcd_Cmd(0x01);

Lcd_Cmd(0x0C);

}

 

void Lcd_Shift_Left()

{

Lcd_Cmd(0x01);

Lcd_Cmd(0x08);

}

 

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