21.4.3.1 Periodic Intervals

The RTC prescaler can generate interrupts and events at periodic intervals, allowing flexible system tick creation. Any of the upper eight bits of the 10-bit prescaler (bits 2 to 9) can be the source of an interrupt or event. When one of the eight Periodic Interval n Event Output Enable bits in the Event Control register (EVCTRL.PEREOn) is ‘1’, an event is generated on the 0-to-1 transition of the related bit in the prescaler (bit n+2), resulting in a periodic event frequency of

fPERIODIC(n)=fCLK_RTC_OSC2n+3

where fCLK_RTC_OSC is the frequency of the internal prescaler clock (CLK_RTC_OSC), and n is the position of the EVCTRL.PEREOn bit. For example, PER0 will generate an event every eight CLK_RTC_OSC cycles, PER1 every 16 cycles, and so on. This is shown in the following figure.

Figure 21-4. Example Periodic Events

Periodic events are independent of the prescaler setting used by the RTC counter, except when the Prescaler bit field in the Control A register (CTRLA.PRESCALER) is configured to OFF. In that case, no periodic events will be generated.