Datasheet

40
XMEGA E5 [DATASHEET]
Atmel-8153J–AVR-ATxmega8E5-ATxmega16E5-ATxmega32E5_Datasheet–11/2014
21. RTC – 16-bit Real-Time Counter
21.1 Features
 16-bit resolution
 Selectable clock source
 32.768kHz external crystal
 External clock
 32.768kHz internal oscillator
 32kHz internal ULP oscillator
 Programmable 10-bit clock prescaling
 One compare register
 One period register
 Clear counter on period overflow
 Optional interrupt/event on overflow and compare match
 Correction for external crystal oscillator frequency error down to ±0.5ppm accuracy
21.2 Overview
The 16-bit real-time counter (RTC) is a counter that typically runs continuously, including in low power sleep modes, to
keep track of time. It can wake up the device from sleep modes and/or interrupt the device at regular intervals.
The reference clock is typically the 1.024kHz output from a high-accuracy crystal of 32.768kHz, and this is the
configuration most optimized for low 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 an external clock signal, the 32.768kHz internal
oscillator or the 32kHz internal ULP oscillator.
The RTC includes a 10-bit programmable prescaler that can scale down the reference clock before it reaches the
counter. A wide range of resolutions and time-out periods can be configured. With a 32.768kHz clock source, the
maximum resolution is 30.5μs, and time-out periods can range up to 2000 seconds. With a resolution of 1s, the
maximum timeout period is more than 18 hours (65536 seconds). The RTC can give a compare interrupt and/or event
when the counter equals the compare register value, and an overflow interrupt and/or event when it equals the period
register value.