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Long time delay using timer

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J

Jack// ani

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Hi all,

Any idea as how to create long time delay using 16f628a timer overflow interrupt, so that cpu is free to do other task? I need some function written in CCS PIC for the same?

Thanks
 

Program the timers to interrupt at its longest reload values, then at the interrupt service routine, increment a variable, if the variable matches your desired time delay, then excute your desired subroutine.
 

Boolean Timeout; // Flag. If true, do whatever you want after the timeout.
static int8 gtimer0_overflow;

#int_timer0
timer0_isr()
{
if (--gtimer0_overflow == 0)
Timeout = TRUE;
}


In your main code, you have to setup the timer0, initialise the global variable gtimer0_overflow.


For example,


setup_timer0(RTCC_INTERNAL|RTCC_DIV_256)
Timeout = FALSE;
gtimer0_overflow = 3; // Variable to control timeout length
enable_interrupts(int_timer0)
enable_interrupts(GLOBAL)

while (!Timeout); // do nothing if Timeout =FALSE


The above example setup a 10 sec delay for PIC18 MCU, 20MHz oscillator. Note that Timer0 is 16 bit for PIC18.
 

Thanks all, I want one of the output port pin to go high for 10sec and then go low 10secs and keep on repeating like this.

Any help.....
 

#int_timer0
timer0_isr()
{
if (--gtimer0_overflow == 0)
{
Timeout = TRUE;
output_toggle(PIN_D1);

}



This will turn PIN_D1 on/off for 10 sec .
 

    J

    Jack// ani

    Points: 2
    Helpful Answer Positive Rating
Hi lguancho,

Thanks a lot for your helpful reply. Output_toggle is very useful function here, but unfortunately it is not mentioned in the CCS PIC help file! I’ve a doubt left,

Will the output be high or low for the first time, when using output_toggle( ) function and how can I change it?

How did you calculate time delay for a single timer overflow cycle?

Thanks again
 

First, you can initialise the output pin to high or low
such as

output_high(PIN_D1) , then you enable the timer1 interrupts. When timer1 overflows, PIN_D1 will be low.

Delay Calculation:

20MHz/4/256= 19531.25Hz=> Timer1 increments every 1/19531.25 sec= 51.2us

Timer1 overflow if it reachs 65536=> 65536X51.2us= 3.3sec

Set the overflow variable to 3, i.e delay= 3x3.3 ~ 10 sec.
 

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