RTC Clock Source

The RTC is commonly used to wake up the device from sleep at periodic intervals. The RTC and its clock are active in Idle, Power-save and Extended standby sleep modes. Hence, RTC can be configured as wake-up source for these sleep modes.

For XMEGA family of devices, three different oscillators can be used to clock the RTC:

External 32 kHz crystal
Internal 32 kHz RC oscillator
Internal 32 kHz Ultra Low Power (ULP) oscillator

In all these cases, a prescaled 1 kHz clock signal is available and should be used for optimized power consumption.

For the external 32 kHz crystal oscillator, a special low-power mode is also available (X32KLPM). It is recommended to use an external 32 kHz crystal with X32KLPM enabled. This gives lower power consumption than the ULP, yet greater accuracy than the internal RC oscillator.

For AVR XMEGA families with the battery backup module and 32-bit RTC, only the 32 kHz crystal oscillator may be used as the clock source. In these devices, the RTC is left running regardless of sleep.

Minimize power consumption by clocking the RTC at 1 kHz with an external crystal in low-power mode.