How to define a 1s timer interrupt

[Memphis]

Hello,

I want to write in C a timer interrupt each 1sec.

I read some examples for my easypic6 board but i don't understand how to do that.
I use a PIC18F4685 with 20MHz oscillator

Someone can help me?

Thanks.

[kada200]

this article might help
http://romanblack.com/one_sec.htm


here's a neat tool for you

http://pictimer.picbingo.com/

[Memphis]

Thanks for all.

I'm not very good in english an in c

The only thing i arrived to do is this:

Code: Select all

// LCD
sbit LCD_RS at LATB4_bit;
sbit LCD_EN at LATB5_bit;
sbit LCD_D4 at LATB0_bit;
sbit LCD_D5 at LATB1_bit;
sbit LCD_D6 at LATB2_bit;
sbit LCD_D7 at LATB3_bit;
sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;
// FIN LCD

unsigned long count;
char txt[12];


void interrupt() {
  if (TMR0IF_bit) {
    count++;
    TMR0IF_bit = 0;        // Clear TMR0IF
  }
}


void main() {
 // OPTION_REG = 0x84;       // Assign prescaler to TMR0

  CMCON = 0x07;            // turn off comparators
  ADCON1 = 0x0F;           // AD-Ports as digital I/O

  count=0;

  Lcd_Init();                        // Initialisation LCD
  Lcd_Cmd(_LCD_TURN_ON);             // Allumage LCD
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Suppression du curseur
  Lcd_Cmd(_LCD_CLEAR);               // Effacement LCD
  Lcd_Out(2,1,"compteur:");
  
  T0CON = 0b11000111;
  INTCON = 0xA0;           // Enable TMRO interrupt

  do {
     LongToStr(count, txt);
     Lcd_Out(3,1,rtrim(txt));
     Lcd_Out(1,1,"wait");
     delay_ms(200);
     Lcd_Out(1,1,"wait.");
     delay_ms(200);
     Lcd_Out(1,1,"wait..");
     delay_ms(200);
     Lcd_Out(1,1,"       ");
     delay_ms(200);

  } while(1);
  
  
}

To initialize the timer0, i try to convert this example for PIC16F to PIC18F:

Code: Select all

unsigned cnt;

void interrupt() {
  if (TMR0IF_bit) {
    cnt++;                 // Increment counter
    TMR0IF_bit = 0;        // Clear TMR0IF
    TMR0   = 96;
  }
}

void main() {
  OPTION_REG = 0x84;       // Assign prescaler to TMR0
  ANSEL  = 0;              // Configure AN pins as digital
  ANSELH = 0;
  C1ON_bit = 0;            // Disable comparators
  C2ON_bit = 0;
  TRISB = 0;               // PORTB is output
  PORTB = 0xFF;            // Initialize PORTB
  TMR0  = 96;              // Timer0 initial value
  INTCON = 0xA0;           // Enable TMRO interrupt
  cnt = 0;                 // Initialize cnt

  do {
    if (cnt >= 400) {
      PORTB = ~PORTB;      // Toggle PORTB LEDs
      cnt = 0;             // Reset cnt
    }
  } while(1);
}

The programm i write for my PIC18F4685 works but the counter is incremented to far...

Thanks for futur help.

[braus]

Hello Memphis, prior to leave interrupt service routine you have to set INTCON.GIE bit to enable future interrupt.

Code: Select all

void interrupt() {
  if (TMR0IF_bit) {
    cnt++;                 // Increment counter
    TMR0IF_bit = 0;        // Clear TMR0IF
    TMR0   = 96;
    INTCON.GIE=1;     //ready
  }
}

[braus]

Another thing, I'm not sure how valid is to use this syntax...

Code: Select all

if (TMR0IF_bit) {   //I mean, you are not explicitly defining that form 
                         //i.e. sbit TMR0IF_bit at INTCON.TMR0IF

...without had declared it previously.

[Memphis]

Hello,

Thanks to read me.

The INTCON.GIE is defined in my main as

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INTCON = 0xA0;
or
INTCON = 0b11100000;

It isn't good?

I try to defining TMR0IF_bit as you say like

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sbit TMR0IF_bit at INTCON.TMR0IF

but it isn't compiling.


So finally i modify this register:

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  T0CON = 0b11000111;
  RCON.IPEN=1;
  INTCON = 0b11100000;

And define my interrupt like this

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void interrupt() {
  if (TMR0IF_bit) {
    co++;
    if( co==77 )
    {
     count++;
     co=0;
    }
    TMR0IF_bit = 0;        // Clear TMR0IF
  }
}

It works fine for the moment, i've got one second timer interrupt...
I don't know if is good... lol

[MARIO]

Hello Memphis, prior to leave interrupt service routine you have to set INTCON.GIE bit to enable future interrupt.

No, it isn't true. You do not need to do this. Once GIE is enabled and returning from interrupt, instruction RETFIE does it automatically.
From the PIC18F4685 datasheet, chapter 9, page 115 :

The “return from interrupt” instruction, RETFIE, exits
the interrupt routine and sets the GIE bit (GIEH or GIEL
if priority levels are used), which re-enables interrupts.

BR.

[Dany]

Another thing, I'm not sure how valid is to use this syntax...

Code: Select all

if (TMR0IF_bit) {   //I mean, you are not explicitly defining that form 
                         //i.e. sbit TMR0IF_bit at INTCON.TMR0IF

...without had declared it previously.

Hi,
The TMR0IF_bit is already declared as

Code: Select all

sbit at INTCON.2;

where

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TMR0IF = 2;

So, TMR0IF_bit is in fact " INTCON.TMR0IF", and can be used as Memphis did...