A real-time clock board based on the DS1307 that interfaces to microcontrollers by I2C. The DS1307 serial real-time clock (RTC) is a low-power, full binary-coded decimal (BCD) clock/calendar that also provides 56 bytes of non-volatile static RAM. Address and data are transferred serially through a bidirectional I2C bus. 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 24-hour or 12-hour format with AM/PM indicator. The DS1307 has a built-in power-sense circuit that detects power failures and automatically switches to the backup supply. Timekeeping operation continues while operaing from the backup supply. The board is designed to plug onto MikroElektronika's PIC development boards, although could also be interfaced to your own circuits or other development boards.