Datasheet

19. RTC – Real-Time Counter

19.1 Overview

The Real-Time Counter (RTC) is a 32-bit counter with a 10-bit programmable prescaler that typically runs

continuously to keep track of time. The RTC can wake up the device from sleep modes using the alarm/

compare wake up, periodic wake up, or overflow wake up mechanisms

The RTC is typically clocked by the 1.024kHz output from the 32.768kHz High-Accuracy Internal Crystal

Oscillator(OSC32K) and this is the configuration optimized for the lowest power consumption. The faster

32.768kHz output can be selected if the RTC needs a resolution higher than 1ms. The RTC can also be

clocked from other sources, selectable through the Generic Clock module (GCLK).

The RTC can generate periodic peripheral events from outputs of the prescaler, as well as alarm/compare

interrupts and peripheral events, which can trigger at any counter value. Additionally, the timer can trigger

an overflow interrupt and peripheral event, and can be reset on the occurrence of an alarm/compare

match. This allows periodic interrupts and peripheral events at very long and accurate intervals.

The 10-bit programmable prescaler can scale down the clock source. By this, a wide range of resolutions

and time-out periods can be configured. With a 32.768kHz clock source, the minimum counter tick

interval is 30.5µs, and time-out periods can range up to 36 hours. For a counter tick interval of 1s, the

maximum time-out period is more than 136 years.

19.2 Features

• 32-bit counter with 10-bit prescaler

• Multiple clock sources

• 32-bit or 16-bit Counter mode

– One 32-bit or two 16-bit compare values

• Clock/Calendar mode

– Time in seconds, minutes and hours (12/24)

– Date in day of month, month and year

– Leap year correction

• Digital prescaler correction/tuning for increased accuracy

• Overflow, alarm/compare match and prescaler interrupts and events

– Optional clear on alarm/compare match

SAM D21 Family

RTC – Real-Time Counter

Datasheet Complete

DS40001882D-page 256