NRF52820-QDAA-R datasheet(231/437 Pages) NORDIC

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Peripherals

Counter increment frequency:

fRTC [kHz] = 32.768 / (PRESCALER + 1 )

The PRESCALER register is read/write when the RTC is stopped. The PRESCALER register is read-only once

the RTC is STARTed. Writing to the PRESCALER register when the RTC is started has no effect.

The PRESCALER is restarted on START, CLEAR, and TRIGOVRFLW, meaning the prescaler value is latched to

an internal register (<<PRESC>>) on these tasks.

Examples of different frequency configurations are as following:

• Desired COUNTER frequency 100 Hz (10 ms counter period)

PRESCALER = round(32.768 kHz / 100 Hz) - 1 = 327

fRTC = 99.9 Hz

10009.576 μs counter period

• Desired COUNTER frequency 8 Hz (125 ms counter period)

PRESCALER = round(32.768 kHz / 8 Hz) – 1 = 4095

fRTC = 8 Hz

125 ms counter period

Prescaler

Counter resolution

Overflow

30.517 μs

512 seconds

28-1

7812.5 μs

131072 seconds

212-1

125 ms

582.542 hours

Table 66: RTC resolution versus overflow

6.14.3 COUNTER register

The COUNTER increments on LFCLK when the internal PRESCALER register (<<PRESC>>) is 0x00.

<<PRESC>> is reloaded from the PRESCALER register. If enabled, the TICK event occurs on each increment

of the COUNTER. The TICK event is disabled by default.

SysClk

LFClk

PRESC

<<PRESC>>

0x000

TICK

COUNTER

0x000002

0x000003

0x000

0x000001

0x000000

Figure 81: Timing diagram - COUNTER_PRESCALER_0

4463_156 v1.0

231

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