EFM32WG Datasheet, PDF (556/834 Pages) List of Unclassifed Manufacturers – The EFM32WG Wonder Gecko is the ideal choice for demanding 8-, 16-, and 32-bit energy sensitive applications.

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21 RTC - Real Time Counter
0123
0123
What?
Quick Facts
The Real Time Counter (RTC) ensures
timekeeping in low energy modes. Combined
with the low power 32.768 kHz oscillator
(XTAL or RC), the RTC can run in EM2 with
total current consumption less than 0.95 µA.
Why?
Timekeeping over long time periods is
required in many applications, while using as
little power as possible.
How?
The 32.768 kHz oscillator is used as clock
signal and the RTC has two different
compare registers that can trigger a wake-up.
24-bit resolution and selectable prescaling
allow the system to stay in EM2 for long a
time and still maintain reliable timekeeping.
21.1 Introduction
The Real Time Counter (RTC) contains a 24-bit counter and is clocked either by a 32.768 kHz crystal
oscillator, or a 32.768 kHz RC oscillator. In addition to energy modes EM0 and EM1, the RTC is also
available in EM2. This makes it ideal for keeping track of time since the RTC is enabled in EM2 where
most of the device is powered down.
Two compare channels are available in the RTC. These can be used to trigger interrupts and to wake
the device up from a low energy mode. They can also be used with the LETIMER to generate various
output waveforms.
21.2 Features
• 24-bit Real Time Counter.
• Prescaler
• 32.768 kHz/2^N, N = 0 - 15.
• Overflow @ 0.14 hours for prescaler setting = 0.
• Overflow @ 4660 hours (194 days) for prescaler setting = 15 (1 s tick).
• Two compare registers
• A compare match can potentially wake-up the device from low energy modes EM1 and EM2.
• Second compare register can be top value for RTC.
• Both compare channels can trigger LETIMER.
• Compare match events are available to other peripherals through the Peripheral Reflex System
(PRS).
21.3 Functional Description
The RTC is a 24-bit counter with two compare channels. The RTC is closely coupled with the LETIMER,
and can be configured to trigger it on a compare match on one or both compare channels. An overview
of the RTC module is shown in Figure 21.1 (p. 557) .
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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