AVR-Chat

hi dears.
i am a new avr user that i should make a digital clock and calender 
for my project.
at the first,i need to make 1 second delay.i have to use timer 
counters but i could make it only for 1 milisecond!
should i use a nother crystal(32.768KH) for it? 
please help me for do this.
thnx alot
bye

koorosh wrote:
> hi dears.
> i am a new avr user that i should make a digital clock and calender 
> for my project.
> at the first,i need to make 1 second delay.i have to use timer 
> counters but i could make it only for 1 milisecond!
> should i use a nother crystal(32.768KH) for it? 
> please help me for do this.
> thnx alot
> bye


In your ISR you need to have a counter, you need to count to 1000, when 
it reaches 1000, you have 1 second.

Regards,

Kat.

On Mon, 25 Jul 2005 07:42:13 -0000 you wrote:

>hi dears.
>i am a new avr user that i should make a digital clock and calender 
>for my project.
>at the first,i need to make 1 second delay.i have to use timer 
>counters but i could make it only for 1 milisecond!
>should i use a nother crystal(32.768KH) for it? 
>please help me for do this.
>thnx alot
>bye

If you have a battery powered project and an AVR with pins for a 32K Xtal then it will save a lot of
power to use it as the AVR can be put in a sleep mode with only the 32K xtal running.
--
Ralph Hilton
http://www.ralphhilton.org
C-Meter: http://www.cmeter.org
FZAOINT http://www.fzaoint.net

--- In AVR-Chat@yahoogroups.com, "koorosh" <koorosh01@y...> wrote:
> hi dears.
> i am a new avr user that i should make a digital clock and calender 
> for my project.
> at the first,i need to make 1 second delay.i have to use timer 
> counters but i could make it only for 1 milisecond!
> should i use a nother crystal(32.768KH) for it? 
> please help me for do this.
> thnx alot
> bye

Whitch Controller? Frequenc??? 
- You can use a 8Mhz Crystal, with a prescale of 256 and a Compare-
Match Interrupt by a countingvalue of 31249 you get an Interrupt every 
second.

73, Florian

hi again

but how can i use counter for 1000,you know ,i could get only 1 
milisecond from 8 bit counter.and how can i make it with 16 bit 
counter?
can you write the codes? what would you do if you have to make 1 
second for a digital clock?

On 25 Jul 2005 at 12:19, koorosh wrote:

> can you write the codes? what would you do if you have to make 1 
> second for a digital clock?

	Study 24 hours a day, perhaps...

thnx dear david and other friends,

On Mon, Jul 25, 2005 at 12:19:13PM -0000, koorosh wrote:
> hi again
> 
> but how can i use counter for 1000,you know ,i could get only 1 
> milisecond from 8 bit counter.and how can i make it with 16 bit 
> counter?
> can you write the codes? what would you do if you have to make 1 
> second for a digital clock?

Its very hard to help when you say so little about what you are using
and what you have done to help yourself.

First you need to study the timer section(s) in the manual for your CPU.
Pay particular attention to the time base options (frequency source) and
available division ratios. On CPUs with timers capable of running off a
2nd crystal at 32 kHz independent of the main system clock it is
practical to produce an overflow interupt once per second.

Is also common to put another counter inside the overflow handler that
one may increase the effective count and measure longer times than the
timer is capable of otherwise. This is something I did on an Atmega64
when during the early stages not all hardware I had to play with had the
32 kHz crystal. So I faked an approximation. Compiler is avr-gcc:

//
//	Timer 0 is 8 bits.
//	Used as a 1 second counter and for software RTC.
//
SIGNAL( SIG_OVERFLOW0 )
{
#ifndef USE_32khz
	//  If not the 32 kHZ clock then must use main CPU XTAL.
	//  Can only divide by 1024 in hardware which still
	//  results in ~61 overflows per second for 16 MHz.
	//  Approximate the seconds clock here.
	static uint8_t subsec;
	
	if( subsec ) {
		subsec--; 
		return;
	}
	subsec = XTAL/1024L/256L;
#endif
	seconds++;

	[ some other things too ]

}

//
//	Do the dirty work to initialize hardware for use of Timer0
//	as a Real Time Clock. Want a 32.768 kHz crystal on TOSC1/2.
//
//	Timer 0 is 8 bits. Config for SIG_OVERFLOW0 exactly 1 Hz.
//
void
t0_init( void )
{
	TIMSK &= ~((1<<TOIE0)|(1<<OCIE0));	//  clear OCIE0 and TOIE0
#ifdef USE_32khz
	ASSR = (1<<AS0);			//  crystal on TOSC1/2
	TCNT0 = 0;
	TCCR0 = (1<<CS02)|(1<<CS00);		//  clock/128 
#else
	ASSR = 0;				//  Use I/O clock
	TCNT0 = 0;				//  seems like a good idea
	TCCR0 = (1<<CS02)|(1<<CS01)|(1<<CS00); //  clock/1024 
#endif
	TIFR  = (1<<TOV0);	//  oddly, writing 1 here clears

	//  Apnote "doc1259.pdf" says we should loop here until not busy:
	//  If this loop doesn't resolve quickly the watchdog will bite.
	while( ASSR & ((1<<TCN0UB)|(1<<OCR0UB)|(1<<TCR0UB)) )
		;

	TIMSK |= (1<<TOIE0);	//  set Timer OVerflow 0 enable
	
}

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.

At 07:19 AM 7/25/2005, koorosh wrote:
>hi again
>
>but how can i use counter for 1000,you know ,i could get only 1
>milisecond from 8 bit counter.and how can i make it with 16 bit
>counter?
>can you write the codes? what would you do if you have to make 1
>second for a digital clock?

I use a 1mS interrupt to count out through weeks in one application.

Set an intermediate counter to increment once a millisecond, and then 
every hundred mS, increment at tenths of seconds counter.
Every time that hits 10, increment the seconds counter, and so on.
When you increment the next counter, zero this one:

In this example, I had a timer interrupt that happened every 5mS

         ;We get here every 5mS

Int_HMS:
         lds             TEMP,HMS                ;Hundred millisec
         dec             TEMP                    ;
         sts             HMS,TEMP                ;
         and             TEMP,TEMP               ;Return if not zero
         breq    Int_HMS_Done                    ;
         ret
Int_HMS_Done:
         ldi             TEMP,20         ;Reload the 100mS (20*5 = 100) counter
         sts             HMS,TEMP                ;

         ;We get here, every 1/10th second

         lds             TEMP,Tenths             ;
         dec             TEMP                    ;
         sts             Tenths,TEMP             ;
         and             TEMP,TEMP               ;
         breq            Int_HMS_Done            ;
         ret
Int_Secs_Done:
         ldi             TEMP,10         ;
         sts             Tenths,TEMP             ;

         lds             TEMP,Seconds            ;
         ;And so on...