Calculating correct seconds value

[Prasapty]

How to precise, count seconds with timer 1 (16Bit ) running on 8 MHZ:

8000000/(4*1*65536) will give 30.51 but then

ints_per_second=30.51

if(sec==60){
sec=0;
}

will give wrong second counting?


main(){
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);
}

[Mark]

Been discussed about a billion times. Try the search feature.

[valemike]

I don't get it. Don't you have a TIMER1 isr

[Prasapty]

I search the forum ( RTC,TIMERS) and most of the post end in my part of the question. Maybe i miss something. Am sorry but i can't find it...

Im using clock_isr()

#INT_TIMER1
void clock_isr()
{

...

}

void main ()
{
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);
...
}

[valemike]

Look at CCS's example code directory at ex_stwt1.c

It shows you how to calculate how many interrupts per second (the example uses 20MHz, but you should be able to calculate it for 8MHz), sets up Timer1 properly, turns on Timer1, and shows a simple ISR. It also shows that you have to enable your timer interrupt to make the isr run.

As for your specific application, you should track your sec variable in your main loop.

[valemike]

From reading your code snippet, you're probably not enabling your timer1 interrupt. It also looks like you're not initializing secs to 0, etc.

[Mark]

I think he is referring to the error encountered from

ints_per_second=30.51

I would use timer2 to do this or use the CCP module (if you have one) to generate an int at a certain count and have the CCP module setup to automatically reset the timer.

[Prasapty]

[MikeValencia]

[Prasapty]

#use delay(clock=8000000)

I changed int_count to BYTE.
The timer1 is now cca 6 seconds SLOWER then real time.

Real time : 0 - 10 -- 16 second

Timer1 : 0 - 10 -- 10 seconds


Is this becuse of the schrinked decimal ( just 2 ) places in the ints_per_second ?

[valemike]

exactly! try #define INTS_PER_SECOND 30 (rather than 30.51).

You cannot assign a float to an int and expect it to get truncated correctly. Otherwise you have to cast it.

[Mark]

You aren't going to be accurrate the way you are doing it. Read my earlier post about the other timers. They would give you the accuracy much easier than trying to do it your ways. in_count should be declared as an int8. It was your reload value that is wrong (as MikeV stated). If you insist on doing it your way, this will give you better accuracy

[Prasapty]

I understand what you want to do and it's allmost unbelivable but...

Real time 0 -- 10 --> 20 seconds
Timer time 0 -- 10 --> 10 seconds

He is now loosing over 10 seconds ( and i have to wait cca 2 second until he starts to count from 0).

Can you point me to your post where you have solved this problem ?

Anyway how is this possible? If you have 61.02 ( 2 seconds_ints ) which should be very near 30.51... How can this be that he is now loosing more time then before ?? I check this 7 times...

[Mark]

Post a complete test program

[Prasapty]

Code test with internal HS on 8 MHZ: