The RTC module is a member of Twig. It is based on the clock chip DS1307 which supports the I2C protocol. It uses a Lithium cell battery (CR1225). 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.

Real-Time Clock (RTC) counts seconds, minutes, hours, date of the month, month, day of the week, and year with Leap-Year compensation valid up to 2100
56-Byte, Battery-Backed, Nonvolatile (NV)RAM for data storage
I2C serial interface
5V DC supply
Programmable Square-Wave output signal
Automatic Power-Fail detect and switch circuitry
Consumes less than 500nA in Battery-Backup Mode with Oscillator Running