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Why unwanted delay is introuduced in Timer1 of PIC16F877A?

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umery2k75

umery2k75

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pic 16f877a timer1 c program

I'm happy with the code, the code works fine and I know the simple logical working of interrupts and how to set the values to get desired response, but the thing which bothers me is that, why Timer 1 starts it's operation very late? I have looked for this thing in it's data sheet too, but I couldn't find anything. If you people know about this, then tell me, but I don't hope that this problem can be answered. I think in this way, because I couldn't find anything on the PIC16F877A datasheet that has a factor which has its effect on Timer1 operation.


I have two codes one that was made around Timer0 8-bit and other was built around Timer1 16-bit.

TIMER 0(8-BIT)
==========

Code: 
#include<16F877A.H>
#include<string.h>
#use delay (clock=03579545)
#fuses   NODEBUG,XT,NOWDT,PUT,NOPROTECT,NOLVP
#use rs232 (baud=2400,xmit=PIN_C6,rcv=PIN_C7)
#define INTS_PER_SECOND 6
int8  int_counts;
int8 ledstate=0;
int8 Hun_Milli_Seconds_Count=0;

#int_rtcc
void clock_isr()
{
   if(--int_counts==0)
      {
         ++Hun_Milli_Seconds_Count;
         int_counts=INTS_PER_SECOND;
      }
}

void main()
{
      set_tris_b(0x00);
      output_low(PIN_B0);
      setup_counters(RTCC_INTERNAL,RTCC_DIV_64);
      enable_interrupts(INT_RTCC);
      enable_interrupts(GLOBAL);
             while(1)
                  {
                              if(Hun_Milli_Seconds_Count==0)   //Makes up approx. a sec
                              {
                                  output_high(PIN_B0);
                                 }

                           if(Hun_Milli_Seconds_Count==1)   //Makes up approx. a sec
                             {
                                  output_low(PIN_B0);
                                   }

                          if(Hun_Milli_Seconds_Count==2)   //Makes up approx. a sec

                                 Hun_Milli_Seconds_Count=0;
                  }

}

As soon as the PIC is power on, I can see the output of PIN_B0 attached by LED turning ON/OFF immediately afterpowering up. I'm happy with it's output.

TIMER 1(16-BIT)
==========

Code: 
#include<16F877A.H>
#include<string.h>
#use delay (clock=03579545)
#fuses   NODEBUG,XT,NOWDT,NOPUT,NOPROTECT,NOLVP
#use rs232 (baud=2400,xmit=PIN_C6,rcv=PIN_C7)
#define INTS_PER_SECOND 1
int8  int_counts;
int8 ledstate=0;
int8  Hun_Milli_Seconds_Count=0;

#int_TIMER1
void clock_isr()
{
   if(--int_counts==0)
      {
         ++Hun_Milli_Seconds_Count;
         int_counts=INTS_PER_SECOND;

      }
}

void main()
{

      set_tris_b(0x00);
      output_low(PIN_B0);

      set_timer1(0);
      setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);   // setup interrupts
      enable_interrupts(INT_TIMER1);
      enable_interrupts(GLOBAL);

             while(1)
                  {
                              if(Hun_Milli_Seconds_Count==0)   //Makes up approx. a sec
                              {
                                  output_high(PIN_B0);
                                 }

                           if(Hun_Milli_Seconds_Count==1)   //Makes up approx. a sec
                             {
                                  output_low(PIN_B0);
                                   }

                          if(Hun_Milli_Seconds_Count==2)   //Makes up approx. a sec

                                 Hun_Milli_Seconds_Count=0;
                  }

}

When PIC is powered on, The ouput PIN_B0 having LED on it, turns ON and it remain On for around 63-64 seconds.After this begins its normal LED blinking work,I don't understand why the interrupt response is getting started too late, why delay is there?

Timer1 seems like a old Diesel engine to me, which is kept at some place in North Pole, which is trying to start on in intense cold. :D

The time is precise, it takes around somewhere 63-64 seconds to turn on



Added after 1 minutes:

Please don't care about the values in the diagram like 109mS and 18.30mS. I made that diagram for some other work.
 

timer1 pic16f877a

Hi,
Assign Int_Count values of 6 for first routine and 1 for second routine in the beginning of the program.

Regards,
Laktronics
 

timer1 coding for pic16f877a

Assign Int_Count values of 6 for first routine and 1 for second routine in the beginning of the program.
Click to expand...

I didn't get your point, what do you mean by first routine and second routine?

If I assign this:

Code: 
int8  int_counts=6;

then to what variable I should assign 1?
 

delay pic16f877a

Hi,
You assign 1 for the same variable in the 16bit timer routine.
Regards,
Laktronics
 

    umery2k75

    umery2k75

    Points: 2
    Helpful Answer Positive Rating
pic16f877 timer1 interrupt

Hi Laktronics,
You know what, the thing which you told me to assign variable int counts=1 just worked perfectly in Timer1 and now my code is working great in Timer1.The first thing I want to say is a BIG THANKS to you and secondly I was thinking what would I do, if you didn't read my post? you wouldn't have replied me and I might have not yet solve this problem.The way you approach this problem was great! Approaching a problem is an art I must say.
According to mathematician George Polya there is a best way to approach a problem and he wrote three books on it :D

Added after 6 minutes:

First thing to notice in my program was that the variable int_counts was not initialized to any constant,so it could have any unknown value in it.

In Timer0 program the variable int_counts must have smaller value like 1,5,etc. So when I runned this program.I just saw the LED working ON/OFF right instantly.

In Timer1 program the variable int_counts must have some big value like 50,60,etc. So when I runned that program I saw the huge delay, then my timer started working properly.
 

timer1 pic16f877

Hi,
Forgetting to initialise the variables is a common problem with C and many times it will not show up since C assigns zero value to those variables. In your case, since you are subtracting first and checking for zero, the variable int_counts becomes INT8 Max value (255) after subtraction and you need so many interrupts before you increment 100_msec register, all along the LED remains ON.

Also, I feel that the LED flashing rate is not same in both the timer cases. If so, you can make it same by using int_counts_persec to 32 in timer 0 program, unless I have missed someyhing else in the code.

Regards,
Laktronics
 

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