Timekeeping

The DS1302 is an 8 pin DIL real time clock that counts seconds , minutes, hours, date of the month, month, day of the week and year with leap year compensation valid up to 2100. Access is via a simple 3 wire serial interface. 8 x 31 RAM, TTL compatible, dual power supply pins for primary backup power supplies, trickle charge capability.
Datasheet

The DS1305 serial alarm real-time clock provides a full binary coded decimal (BCD) clock calendar that is accessed by a simple serial interface. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. In addition, 96 bytes of NV RAM are provided for data storage. An interface logic power-supply input pin (VCCIF) allows the DS1305 to drive SDO and PF-bar pins to a level that is compatible with the interface logic. This allows an easy interface to 3V logic in mixed supply systems.

The DS1305 offers dual-power supplies as well as a battery input pin. The dual power supplies support a programmable trickle charge circuit that allows a rechargeable energy source (such as a super cap or rechargeable battery) to be used for a backup supply. The VBAT pin allows the device to be backed up by a non-rechargeable battery. The DS1305 is fully operational from 2.0V to 5.5V. RoHS compliant.
Datasheet

Datasheet