15.3.2.2 SAM L21/C20/C21 Clock Setup

The RTC clock can be selected from OSC32K, XOSC32K or OSCULP32K , and a 32KHz or 1KHz oscillator clock frequency is required. This clock must be configured and enabled in the 32KHz oscillator controller before using the RTC.

Table 15-3 lists the available RTC clock.

Table 15-3. RTC Clocks Source

RTC clock frequency

Clock source

Description

1.024kHz

ULP1K

1.024kHz from 32KHz internal ULP oscillator

32.768kHz

ULP32K

32.768kHz from 32KHz internal ULP oscillator

1.024kHz

OSC1K

1.024kHz from 32KHz internal oscillator

32.768kHz

OSC32K

32.768kHz from 3KkHz internal oscillator

1.024kHz

XOSC1K

1.024kHz from 32KHz internal oscillator

32.768kHz

XOSC32K

32.768kHz from 32KHz external crystal oscillator

Note: For the calendar to operate correctly, an asynchronous clock of 1Hz should be used.