The DS1307 is a low power, with 56 bytes of non-volatile RAM BCD code clock calendar real-time clock chip, the address and data transmission through the two-wire bidirectional serial bus, the chip can be seconds, minutes, hours and other information , the number of days in each month can be adjusted automatically. And there is a leap year compensation function. AM / PM flag determines clock work 24-hour or 12-hour mode, the chip has a built-in power-sense circuit, brownout detection and battery switching function.