How can I use Timer0 on PIC16F877A ?

[bianchi77]

Hello friends,

Does anyone know on how can I use Timer0 on PIC16F877A ?
I'm using Hi-Tech C.

Thanks

 

[Jestin_cubetech]

for interrupt TMR0IE=1;
TMR0IF flag bit
TMR0 8bit timer register

 

[themask]

IMHO, you are asking a general question.

Which one do you want to know first?
- special function registers
- block diagram/operation
- timer mode/counter mode
- use of prescalers
- interrupt operation
- calculating interrupt rate
- using preset values
- skip timer technique for multitasking

It is always nice to read the datasheet first, just 3-4 pages i think. Understand how TMR0 works by referring to the block diagram

 

[jayanth.devarayanadurga]

It depends upon how much delay you want and your Fosc.

 

[bianchi77]

for example I want to create 1 second delay for timer 0.....
do you guys have an example code ?
For a example I blink LED on portd bit 0, every 1 second....
so RD0 = ~RD0 every 1 second, how can I set the timer0 for it ?

Thanks

I got this one from Hi Tech C example but I don't know yet on how to use it...

timer0_isr(void)
{
	if(reload == 0){
		// effect a change on PORTB whenever our desired period is reached.
		// Note this timing will contain a margin of error.
		reload = RELOADS + 1;
		seconds++;
		PORTD++;	// effect a change on PORTB
	}
	reload--;
	T0IF = 0;
}

main()
{
	// initialize timer 0; 
	
	//OPTION = 0b0111;	// prescale by 256
	T0CS = 0;			// select internal clock
	T0IE = 1;			// enable timer interrupt
	GIE = 1;			// enable global interrupts
	TRISD = 0;			// output changes on LED
    PORTD = ~PORTD;
   
	for(;;)
		continue;		// let interrupt do its job
    PORTD = 1;
}

 

[jayanth.devarayanadurga]

PIC16F877A, Fosc = 4 MHz, 10 ms * 100 = 1000 ms timer

---

Code C - [expand]
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unsigned char time = 0, timerflag = 0;
 
//Timer0
//Prescaler 1:64; TMR0 Preload = 97; Actual Interrupt Time : 9.986 ms
 
//Place/Copy this part in declaration section
void InitTimer0(){
  OPTION_REG     = 0x85;
  TMR0       = 97;
  INTCON     = 0xA0;
}
 
void Interrupt(){
  if (TMR0IF_bit){ 
    TMR0IF_bit   = 0;
    TMR0     = 97;
    TMR0IE_bit = 0;
    //Enter your code here
    time++;
    if(time == 100){
    timerflag = 1;
    }
 
    
  }
}
 
void main(){
        TRISD = 0x00;
        PORTD = 0x00;
        LATD = 0x00;
 
        InitTimer0()
 
    while(1){
 
        if(timerflag == 1){
            timerflag = 0;
            PORTD = ~PORTD;
        }
    }
 
}

---

 

[bianchi77]

PIC16F877A, Fosc = 4 MHz, 10 ms * 100 = 1000 ms timer

---

Code C - [expand]
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unsigned char time = 0, timerflag = 0;
 
//Timer0
//Prescaler 1:64; TMR0 Preload = 97; Actual Interrupt Time : 9.986 ms
 
//Place/Copy this part in declaration section
void InitTimer0(){
  OPTION_REG     = 0x85;
  TMR0       = 97;
  INTCON     = 0xA0;
}
 
void Interrupt(){
  if (TMR0IF_bit){ 
    TMR0IF_bit   = 0;
    TMR0     = 97;
    TMR0IE_bit = 0;
    //Enter your code here
    time++;
    if(time == 100){
    timerflag = 1;
    }
 
    
  }
}
 
void main(){
        TRISD = 0x00;
        PORTD = 0x00;
        LATD = 0x00;
 
        InitTimer0()
 
    while(1){
 
        if(timerflag == 1){
            timerflag = 0;
            PORTD = ~PORTD;
        }
    }
 
}

---

Thank you for the info I'll make it now and see what happens, I'll get back soon

- - - Updated - - -

PIC16F877A, Fosc = 4 MHz, 10 ms * 100 = 1000 ms timer

---

Code C - [expand]
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unsigned char time = 0, timerflag = 0;
 
//Timer0
//Prescaler 1:64; TMR0 Preload = 97; Actual Interrupt Time : 9.986 ms
 
//Place/Copy this part in declaration section
void InitTimer0(){
  OPTION_REG     = 0x85;
  TMR0       = 97;
  INTCON     = 0xA0;
}
 
void Interrupt(){
  if (TMR0IF_bit){ 
    TMR0IF_bit   = 0;
    TMR0     = 97;
    TMR0IE_bit = 0;
    //Enter your code here
    time++;
    if(time == 100){
    timerflag = 1;
    }
 
    
  }
}
 
void main(){
        TRISD = 0x00;
        PORTD = 0x00;
        LATD = 0x00;
 
        InitTimer0()
 
    while(1){
 
        if(timerflag == 1){
            timerflag = 0;
            PORTD = ~PORTD;
        }
    }
 
}

---

do you have the calculation or description of it ?
thanks

- - - Updated - - -

I got these errors with the code above

Error   [192] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 16.5 undefined identifier "TMR0IF_bit"
Error   [192] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 19.1 undefined identifier "TMR0IE_bit"
Error   [192] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 33.1 undefined identifier "LATD"
Error   [312] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 37.1 ";" expected
Error   [285] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 43.1 no identifier in declaration
Warning [374] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 43.1 missing basic type; int assumed
Error   [314] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 43.1 ";" expected
Error   [285] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 45.1 no identifier in declaration
Warning [374] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 45.1 missing basic type; int assumed
Error   [314] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 45.1 ";" expected

- - - Updated - - -

I defined as char

char TMR0IF_bit,TMR0IE_bit;

but get :

Error   [192] C:\Users\Antonius\Documents\MPLAB\LCD16X2\LCD_with_timer.c; 35.1 undefined identifier "LATD"

for the time being, I commented out LATD

- - - Updated - - -

I can't see a proper result for the timer, anyone can help me ? thanks

 

[jayanth.devarayanadurga]

Change TMR0IF_bit and TMR0IE_bit to TMR0IF and TMR0IE. If it doesn't work then use INTCONbits.TMR0IF and INTCONbits.TMR0IE. Put ; semi-colon after InitTimer0() function call. Remove LATD line, you don't need it.

 

[bianchi77]

Change TMR0IF_bit and TMR0IE_bit to TMR0IF and TMR0IE. If it doesn't work then use INTCONbits.TMR0IF and INTCONbits.TMR0IE. Put ; semi-colon after InitTimer0() function call. Remove LATD line, you don't need it.

Ok, I'll try, I'll let you know the progress..
thanks