Atmel AVR XMEGA 8/16-bit High Performance Low Power Flash Microcontrollers Datový list stáhnout pdf (Strana 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

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Atmel AVR XMEGA 8/16-bit High Performance Low Power Flash Microcontrollers Datový list Strana 40