Timer1 interrupt is not serving first...

[Prashant Patel]

Hi...I am using 16F877 with 20MHz oscillator

I have a Timer1 interrupt which is generating 20mSec
pulse with 30% duty cycle.
And I have one buttun, and the code for identifying
button press is put inside the main()-->while() loop.

Now when ever I press the Mode Button for some seconds
then Timer1 generating one big pulse instead of the
20mSec pulse.

Even though the Timer1 is an interrupt, why it is not
generating the exact pulses.
The code is as below:
-----------------------------------------------------
signed int8 count1,DCOnDuty=30;

#INT_TIMER1
void timer1_isr() {

set_timer1(64536);

if(count1<=DCOnDuty)
output_high(PIN_D0);
else
output_low(PIN_D0);

count1++;

if(count1>=100)
count1=0;

}//timer1_isr


void UpButton()
{
// Some code for Up Button press.
//If we press this button for some seconds,it should
//not change the interrupt time for Timer1. But is it
//affecting it...why..???
}
void main() {

set_tris_d(0x00);
set_tris_b(0xFF);

while(TRUE)
{

if(!input(PIN_B1))
{
delay_ms(20);
UpButton();
}
}
}
-----------------------------------------------------

Thanks...any guidance appreciated....

Regards
Prashant

[Haplo]

You might need to post your full code as a few important questions can't be answered by looking at what you have posted. Such as

-How are you setting up the Timer and the interrupts?
-Is the button-checking code also interrupt driven?
-Does the button-checking code disable the interrupts by any chance?
-The variables count1 and DCOnDuty are globals. Is there any chance that they get modified by UpButton() ?