#include <Wire.h>
#include <avr/pgmspace.h>
#define WIRE Wire
#define DS1307_ADDRESS  0x68
#if (ARDUINO >= 100)
 #include <Arduino.h> // capital A so it is error prone on case-sensitive filesystems
 // Macro to deal with the difference in I2C write functions from old and new Arduino versions.
 #define _I2C_WRITE write
 #define _I2C_READ  read
#else
 #include <WProgram.h>
 #define _I2C_WRITE send
 #define _I2C_READ  receive
#endif

static uint8_t bcd2bin (uint8_t val) { return val - 6 * (val >> 4); }
static uint8_t bin2bcd (uint8_t val) { return val + 6 * (val / 10); }


void setup(){
  Serial.begin(9600);
}

void loop(){
  WIRE.beginTransmission(DS1307_ADDRESS);
  WIRE._I2C_WRITE(0);
  WIRE.endTransmission();
  WIRE.requestFrom(DS1307_ADDRESS, 7);
  uint8_t ss = bcd2bin(WIRE._I2C_READ() & 0x7F);
  uint8_t mm = bcd2bin(WIRE._I2C_READ());
  uint8_t hh = bcd2bin(WIRE._I2C_READ());
  WIRE._I2C_READ();
  uint8_t d = bcd2bin(WIRE._I2C_READ());
  uint8_t m = bcd2bin(WIRE._I2C_READ());
  uint16_t y = bcd2bin(WIRE._I2C_READ()) + 2000;
  Serial.print(y);
  Serial.print("-");
  Serial.print(m);
  Serial.print("-");
  Serial.print(d);
  Serial.print(" ");
  Serial.print(hh);
  Serial.print(":");
  Serial.print(mm);
  Serial.print(":");
  Serial.println(ss);
  delay(1000);
}