Re: [avr-chat] Re:

[Anton Erasmus]

On 1 Dec 2007 at 15:52, Dharmesh Joshi wrote:

From:   "Dharmesh Joshi" <address@hidden>
To:     <address@hidden>
Date sent:      Sat, 1 Dec 2007 15:52:04 -0000
Subject:        [avr-chat] Re:

> Hi Guys
> 
> The AVR has in built timers, are there any samples code or website showing 
> how to use them.  I am very interested in using them as a calendar,  and 
> passing there varaible to my program and also changing the calander when 
> nessary.
> 

If you want time and calender functions, then you should use a RTC (Real Time 
Clock). 
Some of the AVRs do have the functionality to enable one to add a "watch 
crystal" which is a
32.768kHz crystal which is often used to provide the clock for RTC functions. 
It is simpler to use a dedicated RTC device.

Below is a routine  for calculating the weekday from a specific date:

/********************************************************************\
* Calculate Day of the week
* 0 -> SUN
* 6 -> SAT
\********************************************************************/
unsigned char GregorianWeekDay(unsigned short year, unsigned char month, 
unsigned char 
day)
{
  int a,y,m,d;

  a = (14 - month) / 12;
  y = year - a;
  m = month + 12*a - 2;
  d = (day + y + y/4 - y/100 + y/400 + (31*m)/12) % 7;
  return((unsigned char)d);
} 

Regards
  Anton Erasmus
-- 
A J Erasmus