#include <Wire.h>

#define DS1307_ADDRESS 0x68 /* I2C address of the DS1307 RTC */
#define SECONDS_REGISTER 0x00
#define MINUTES_REGISTER 0x01
#define HOURS_REGISTER 0x02
#define DAY_REGISTER 0x03
#define DATE_REGISTER 0x04
#define MONTH_REGISTER 0x05
#define YEAR_REGISTER 0x06


uint8_t RTC_Mem[8];  /* Memory for the RTC */
uint8_t* ptrRTCmem;

void readRTC(void) {
  uint8_t i;
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire.write(SECONDS_REGISTER); /* Start at the seconds register */
  Wire.endTransmission();
  
  Wire.requestFrom(DS1307_ADDRESS, 7); /*  Request 7 bytes */
  
  for(i=0; i<7; i++){
    RTC_Mem[i] = Wire.read();  
  }
}

void setup() {
  Wire.begin(); /* Start I2C communication */
  Serial.begin(9600); /* Start serial communication for debugging */
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire.write(SECONDS_REGISTER); /* Start at the seconds register */
  Wire.write(0x00);
  Wire.endTransmission();

  ptrRTCmem = &RTC_Mem[SECONDS_REGISTER]; /* Point at the beginning */
}

void loop() {
  uint8_t temp;
  readRTC();

  Serial.print("Local Time: ");
/* hours */
  temp = *(ptrRTCmem + HOURS_REGISTER);
  temp = (temp >> 4) * 10 + (temp & 0x0F);
  Serial.print(temp);
  Serial.print(":");

/* minutes */
  temp = RTC_Mem[MINUTES_REGISTER];
  temp = (temp >> 4) * 10 + (temp & 0x0F);
  Serial.print(temp);

/* seconds */
  temp = *(ptrRTCmem + SECONDS_REGISTER) & 0x7F;
 /*temp = RTC_Mem[SECONDS_REGISTER] & 0x7F;*/
  temp = (temp >> 4) * 10 + (temp & 0x0F);
  Serial.print(":");
  Serial.println(temp);
  
  delay(1000); /* Wait for 1 second before updating the time again */
}