NRF52820-QDAA-R7 datasheet(70/437 Pages) NORDIC

70 / 437 page

Power and clock management

LFCLKSTART

HFCLKSTART

LFCLKSTOP

HFCLKSTOP

LFCLKSTARTED

HFCLKSTARTED

CLOCK

32.768 kHz

32 MHz

LFCLK

Clock control

XL1

XL2

HFCLK

Clock control

XC1

XC2

CAL

SYNT

LFXO

Crystal oscillator

HFXO

Crystal oscillator

PCLK32KI

PCLK1M

PCLK16M

HCLK64M

LFRC

RC oscillator

HFINT

Internal oscillator

PCLK32M

Figure 20: Clock control

5.4.1 HFCLK controller

The HFCLK controller provides several clock signals in the system.

These are as follows:

• HCLK64M: 64 MHz CPU clock

• PCLK1M: 1 MHz peripheral clock

• PCLK16M: 16 MHz peripheral clock

• PCLK32M: 32 MHz peripheral clock

The HFCLK controller uses the following high frequency clock (HFCLK) sources:

• 64 MHz internal oscillator (HFINT)

• 64 MHz crystal oscillator (HFXO)

For illustration, see Clock control on page 70.

The HFCLK controller will automatically provide the clock(s) requested by the system. If the system does

not request any clocks from the HFCLK controller, the controller will enter a power saving mode.

The HFINT source will be used when HFCLK is requested and HFXO has not been started.

The HFXO is started by triggering the HFCLKSTART task and stopped by triggering the HFCLKSTOP task.

When the HFCLKSTART task is triggered, the HFCLKSTARTED event is generated once the HFXO startup

time has elapsed. The HFXO startup time is given as the sum of the following:

• HFXO power-up time, as specified in 64 MHz crystal oscillator (HFXO) on page 82.

• HFXO debounce time, as specified in register HFXODEBOUNCE on page 81.

The HFXO must be running to use the RADIO or the calibration mechanism associated with the 32.768 kHz

RC oscillator.

4463_156 v1.0

NRF52820-QDAA-R7 Datasheet(PDF) 70 Page - Nordic Semiconductor

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