ATXMEGA384C3_14 Datasheet, PDF (37/125 Pages) ATMEL Corporation – 8/16-bit Atmel XMEGA C3 Microcontroller

20. RTC – 16-bit Real-Time Counter
20.1
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
20.2
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 than18 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.
Figure 20-1. Real-time Counter Overview
TOSC1
TOSC2
External Clock
32.768kHz Crystal Osc
32.768kHz Int. Osc
32kHz int ULP (DIV32)
RTCSRC
clk_RTC
10-bit
prescaler
PER
=
CNT
=
COMP
TOP/
Overflow
”match”/
Compare
XMEGA C3 [DATASHEET]
37
Atmel-8361F-AVR-ATxmega384C3-Datasheet–11/2014