void TWI_start();
void TWI_stop();
void TWI_write(char);
char TWI_read();
void RTC_write(char,char);
char RTC_read(char);

void setup() {
  volatile char *TWBR1=(volatile char*) 0xB8;
  *TWBR1=0x48;//for 100khz scl 
   volatile char *TWSR1=(volatile char*) 0xB9;
   *TWSR1=0x00;//prescalar is 1;
   Serial.begin(9600);
   RTC_write(0x00,0x30);
RTC_write(0x01,0x30);
RTC_write(0x02,0x17);
while(1)
{
char second=RTC_read(0x00);
char minute=RTC_read(0x01);
char hour=RTC_read(0x02);
Serial.print("Time :");
Serial.print(hour,HEX);
Serial.print("/");
Serial.print(minute,HEX);
Serial.print("/");
Serial.println(second,HEX);
delay(1000);
}
}

void RTC_write(char address,char data)
{
TWI_start();
TWI_write(0xD0);
TWI_write(address);
TWI_write(data);
TWI_stop();
}

char RTC_read(char address)
{
TWI_start();
TWI_write(0xD0);
TWI_write(address);
TWI_start();
TWI_write(0xD1); 
char data=TWI_read();
TWI_stop();
return data;
}


void TWI_start()
{
  volatile char *TWCR1=(volatile char*) 0xBC;
  *TWCR1=0xA4;//set start bit 
  while(!(*TWCR1 & (0x80)));
}

 void TWI_write(char data)
 {
 volatile char *TWCR1=(volatile char*) 0xBC;
  volatile char *TWDR1=(volatile char*) 0xBB;
    *TWDR1=data;
    *TWCR1=0x84;
while(!(*TWCR1 & (0x80)));
 }

  void TWI_stop()
  {
 volatile char *TWCR1=(volatile char*) 0xBC;
  *TWCR1=0xB4;//set stop bit 
  while(!(*TWCR1 & (0x80)));
  }

  char TWI_read()
  {
 volatile char *TWCR1=(volatile char*) 0xBC;
  volatile char *TWDR1=(volatile char*) 0xBB;
    *TWCR1=0x84;
while(!(*TWCR1 & (0x80)));
 char data =*TWDR1;
 return data;
  }

void loop() {
  // put your main code here, to run repeatedly:

}