This highlights the key features of the RTC block. The block measures the passage of time to maintain a calendar and clock; provides seconds, minutes, hours, day of month, month, year, day of week, and day of year; and has ultra-low power design to support battery powered systems. Less than 1µA is required for battery operation and uses power from the CPU power supply when it is present. The dedicated 32 KHz ultra low power oscillator also has a dedicated battery power supply pin that is isolated from the rest of the chip. The RTC will work down as low as 2.1V.