#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include "LCD.c"
 
#define F_CPU 8000000UL
#define HOUR                (*(unsigned char *) (0x4F0))     // 01
#define MINUTE              (*(unsigned char *) (0x4F1))     // 02
#define SECOND              (*(unsigned char *) (0x4F2))     // 03
#define DAY                 (*(unsigned char *) (0x4F3))     // 04
#define MONTH               (*(unsigned char *) (0x4F4))     // 05
#define YEAR_HI             (*(unsigned char *) (0x4F5))     // 06
#define YEAR_LO             (*(unsigned char *) (0x4F6))     // 07
#define FALSE   0
#define TRUE    1
 
 
// Lookup table used to determine the highest date in a specific month
unsigned char MaxDate[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 
 
/*! \brief  Start Timer/Counter2 in asynchronous operation using a
 *          32.768kHz crystal.
 */
void RTC_init(void)
{
 
 
cli();  // disabel global interrupt
 
TCCR0 = (1<<CS02) | (1<<CS00); // select precaler: 32.768 kHz / 128 = 1 
//sec between each overflow
 
    TIMSK = 0; // disable OCIE0 and TOIE0
 
    ASSR = (1<<AS0); // select asynchronous operation of Timer0
 
    TCNT0 = 0; // clear TCNT0
 
    while(ASSR & (0x01 | 0x04)==0); // wait for TCN0UB and TCR0UB to be cleared
 
    TIFR = 0xFF; // clear interrupt-flags
    TIMSK = (1<<TOIE0); // enable Timer0 overflow interrupt
 
   sei(); // enable global interrupt
 
    // initial time and date setting
    HOUR = 23;
    MINUTE = 59;
    SECOND = 58;
    DAY = 31;
    MONTH = 02;
    YEAR_LO = 12;
    YEAR_HI = 20;
}
 
 
/*! \brief  Updates the time and date variables
 */
void Time_update(void)
{
   unsigned char LeapYear = FALSE;
 
    //the variable SECOND gets updated in the Timer0 
//Overflow Interrupt Routine every second
 
    if(SECOND > 59) // if one minute
    {
        SECOND = 0;  // clear SECOND
        MINUTE++;   // increment MINUTE
 
        if(MINUTE > 59) // if one hour
        {
            MINUTE = 0; // clear MINUTE
            HOUR++;  // increment HOUR
 
            if(HOUR > 23) // if one hour
            {
                HOUR = 0; // clear HOUR
                DAY++;  // increment DAY
 
                if(MONTH == 2) // if it's February
                {
                    // check for leap year
                    if(!YEAR_LO) // if YEAR_LO = 0, (a century has passed)
                    {
                        if(!(YEAR_HI%4))// check if YEAR_HI is divisible by 4
                            LeapYear = TRUE; // then it is a leap year
                    }
                    else if(!(YEAR_LO%4) & (YEAR_LO != 0))  
// else if YEAR_LO is divisible by 4 and not zero
                LeapYear = TRUE; // then it's a leap year
                }
 
                if(DAY > (MaxDate[MONTH] + LeapYear))   // if a whole month has passed
                {
                    DAY = 1; // clear DAY
                    MONTH++; // increment MONTH
 
                    if(MONTH > 12) // if one year
                    {
                    MONTH = 1; // clear MONTH
                    YEAR_LO++; // increment YEAR_LO
 
                    if(YEAR_LO > 99) // if one century
                    {
                    YEAR_LO = 0; // clear YEAR_LO
                    YEAR_HI++;  // increment YEAR_HI
 
                    if(YEAR_HI > 99) // if 100 centuries
                    YEAR_HI = 0; // the AVR is still going strong :)
                    }
                  }
               }
           }
       }
   }
}
 
 
/*! \brief  Increment the varible SECOND by one - interrupt function.
 */
ISR(TIMER0_OVF_vect) 
{
unsigned char key[10]=	{'0','1','2','3','4','5','6','7','8','9'};
 
unsigned char sec_des,sec_ed,min_des,min_ed,hour_des,hour_ed;
unsigned char day_des,day_ed,mon_des,mon_ed,year_th,year_hand,year_des,year_ed;  
 
	hour_des=HOUR/10;hour_ed=HOUR-hour_des*10;		
	min_des=MINUTE/10;min_ed=MINUTE-min_des*10 ;	
	sec_des=SECOND/10;sec_ed=SECOND-sec_des*10 ;
	day_des=DAY/10;day_ed=DAY-day_des*10;
	mon_des=MONTH/10;mon_ed=MONTH-mon_des*10;
	year_th=YEAR_HI/10;year_hand=YEAR_HI-year_th*10;
	year_des=YEAR_LO/10;year_ed=YEAR_LO-year_des*10;
 
 
	lcd_com(0x80); //Ставим курсор на первую строку
	lcd_dat(key[hour_des]);
	lcd_dat(key[hour_ed]);
	lcd_dat(0x3A);
	lcd_dat(key[min_des]);
	lcd_dat(key[min_ed]);
	lcd_dat(0x3A);
	lcd_dat(key[sec_des]); 
	lcd_dat(key[sec_ed]);
 
	lcd_com(0xC0);
	lcd_dat(key[day_des]);
	lcd_dat(key[day_ed]);
	lcd_dat(0x2E);
	lcd_dat(key[mon_des]);
	lcd_dat(key[mon_ed]);
	lcd_dat(0x2E);
	lcd_dat(key[year_th]); 
	lcd_dat(key[year_hand]);
	lcd_dat(key[year_des]); 
	lcd_dat(key[year_ed]);
 
	 SECOND++; // increment second			
	}
 
void main (void)
{   
RTC_init();
lcd_init();
sei();
while(1)
 {
 Time_update();
 }
}