#include <Wire.h>

#define DS1307_ADDRESS 0x68 /* I2C address of the DS1307 RTC */
#define SECONDS_REGISTER 0x00

typedef union {
  uint8_t bcd_value;
  struct {
    uint8_t units :4, /* decenas */
            tents :4; /* unidades */
  } nibble;
} RTC_item_type;

typedef union {
  uint8_t content[8];
  struct {
    RTC_item_type seconds;
    RTC_item_type minutes;
    RTC_item_type hours;
    uint8_t day;
    uint8_t date;
    uint8_t month;
    uint8_t year;
    uint8_t ram;
  } regs;
} RTC_type;

RTC_type rtc_mem;

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<8; i++){
    rtc_mem.content[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();
}

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

  Serial.print("Local Time: ");


  temp = (rtc_mem.regs.hours.nibble.tents & 0x3F) *10 + rtc_mem.regs.hours.nibble.units;
  Serial.print(temp);
  Serial.print(":");

  temp = 0;
  Serial.print(temp);

  temp = (rtc_mem.regs.seconds.nibble.tents & 0x7F) *10 + rtc_mem.regs.seconds.nibble.units;
  Serial.print(":");
  Serial.println(temp);
  
  delay(1000); /* Wait for 1 second before updating the time again */
}