Need help programming timer interrupt for PIC16F877A

[ccslearner]

Hai friends, first of all i want tell one thing i am more happy to member of these website because the objective of the forum is more attracted and also this is my firs post along a long period of searching, my question is
1) any one can help me to write the LED blinking program like the order of given below
LED1 ON 2sec and OFF 5 sec
LED2 ON 3sec and OFF 6sec using Timer2 Interrupt(the interrupt is created every 5msec)

I am using PIC16F877A mcu and CCS compiler to work above assignment and i have the code for timer2 interrupt to LED1 ON 2sec and OFF 2sec , LED2 ON 5sec and OFF 5sec(symmetric) these code was working but i cant to modify the program to get output (asymmetric wise) like above my question . I hope more answer

thanks

 

[jayanth.devarayanadurga]

Post your code.

You have to use this code for 5 ms Timer 2 Interrupt

---

Code C - [expand]
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//Timer2
//Prescaler 1:16; Postscaler 1:7; TMR2 Preload = 223; Actual Interrupt Time : 4.9966 ms
 
//Place/Copy this part in declaration section
void InitTimer2(){
  T2CON  = 0x36;
  PR2        = 223;
  TMR2IE_bit     = 1;
  INTCON     = 0xC0;
}
 
void Interrupt(){
  if (TMR2IF_bit){ 
    TMR2IF_bit = 0;
    //Enter your code here
  } 
}

---

You have to use a 4 counters and flag in interrupt routine. Each counter wil have to be reset after reaching its max value and a flag has to be set. If the flag is set you call the blinking routine in main function.

counter max values are like this

2 sec count = 400
3 sec count = 600
5 sec count = 1000
6 sec count = 1200

My values are for 20 MHz crystal. What Clock are you using?

 

[manikandanshine]

can you post ur code?

 

[ccslearner]

Yes friends

#include <timer interrupt.h>

#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)


int1 two_sec_timer_flag = FALSE,five_sec_timer_flag =FALSE,ten_sec_timer_flag = FALSE ;
int16 two_sec_count,five_sec_count,ten_sec_count;

#INT_TIMER2
void timer2_isr()
{
two_sec_count++;
five_sec_count++;
ten_sec_count++;
{
if(two_sec_count == 400) // 400 * 5 msec = 2000 msec = 2 sec
{
two_sec_count = 0;
two_sec_timer_flag = TRUE;
}
if(five_sec_count==1000) /// 1000 * 5 msec = 5000 msec = 5 sec
{
five_sec_count=0;
five_sec_timer_flag=TRUE;
}
if(ten_sec_count == 2000) // 2000 * 5 =10000 msec = 10 sec
{
ten_sec_count = 0 ;
ten_sec_timer_flag = TRUE;
}
}
}
void main ()
{
int1 last_2sec,last_5sec,last_10sec;

//setup_timer_2(T2_DIV_BY_4,78,16);//setup up timer2 to interrupt every 1ms
setup_timer_2(T2_DIV_BY_4,250,5); //setup up timer2 to interrupt every 1ms
//setup_timer_2 (mode, period, post scale)
//mode - T2_DISABLED, T2_DIV_BY_1, T2_DIV_BY_4, T2_DIV_BY_16
//period is a int 0-255 that determines when the clock value is reset,
//post scale is a number 1-16 that determines how many timer overflows before
//an interrupt: (1 means once, 2 means twice, and so on).

// calculating timer reload value to generate 1 msec interrupt
// T = 1/f
// T = 1/4MHZ = 1/4* 1000000
// But Microcontroller hardware will divide the clock by 4
// and if we chosen T2_DIV_BY_4 then again there will
// one more division happen by 4
// So T = 1/(4 * 1000000)/ 4 * 4 / T=4/4*1000000
// T = 4*4/4*1000000 = 0.000004 sec = 0.4 usec //4 usec
// ************************************************
// At4mhz, the timer will increment every 0.4 us // 4 usec *// 0.000004 sec
// ************************************************

// ********************************************************
// if period is chosen 250 then timer wi
//ll overflow every *
// 4 * 250 = 1000 usec //1 msec *
// ********************************************************

// *******************************************************************
// And if we chosen post scalar as 5 then timer interrupt will occur *
//1000 usec * 5 = 5000 usec /// 5 msec
// *******************************************************************
last_2sec=FALSE;
last_5sec=FALSE;
last_10sec=FALSE;
enable_interrupts(INT_TIMER2); // enable timer2 interrupt
enable_interrupts(GLOBAL);
output_b(0x0); // off all theLEDS
putc('z');
//infine loop
while (1)
{

if( two_sec_timer_flag == TRUE)
{
two_sec_timer_flag = FALSE;
//printf("I am in 2 sec \n\r");

last_2sec = ~last_2sec;
if ( last_2sec == TRUE)
{
output_b( (input_b() | 0x01)); // ON LED 1 alone
}
else
{
output_b( (input_b() & 0xFE)); // OFF LED 1 alone
}

}
if( five_sec_timer_flag == TRUE )
{
five_sec_timer_flag = FALSE;
// printf ("I am in 5 sec \n\r" );
last_5sec = ~last_5sec;
if ( last_5sec == TRUE)
{
output_b( (input_b() | 0x02)); // ON LED 2 alone
}
else
{
output_b( (input_b() & 0xFD)); // OFF LED 2 alone
}

}
if( ten_sec_timer_flag == TRUE)
{
ten_sec_timer_flag = FALSE;
//printf("i am in 10 sec \n\r");
last_10sec = ~last_10sec;
if(last_10sec==TRUE)
{
output_b( (input_b() | 0x04) ); // ON LED3 alone
}
else
{
output_b( (input_b() & 0xFB)); // OFF LED 3 alone
}






} // end of while


} // end of main

}

- - - Updated - - -

anyone cite me the small change of code and i am in beginning stage of embedded c

 

[jayanth.devarayanadurga]

This code is for 4 MHz clock

---

Code C - [expand]
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//Timer2
//Prescaler 1:4; Postscaler 1:5; TMR2 Preload = 250; Actual Interrupt Time : 5.005 ms
 
//Place/Copy this part in declaration section
void InitTimer2(){
  T2CON  = 0x25;
  PR2        = 250;
  TMR2IE_bit     = 1;
  INTCON     = 0xC0;
}
 
void Interrupt(){
  if (TMR2IF_bit){ 
    TMR2IF_bit = 0;
    //Enter your code here
  } 
}

---

Edit your last post and post the code in between code or syntax tags.

 

[ccslearner]

thanks to reply I am using PIC16F877A mcu ,my clock value is 4 MHz

 

[jayanth.devarayanadurga]

See my last post.

 

[ccslearner]

sorry can you replace to your code in my post that is the way i understand better

 

[jayanth.devarayanadurga]

I haven't used CCS C. You can use the timer values in my code to setup your CCS C timer code.