NRF52811-QCAA-R datasheet(62/444 Pages) NORDIC

62 / 444 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 17: Clock control

5.4.1 HFCLK clock controller

The HFCLK clock controller provides the following clocks to the system.

• HCLK64M: 64 MHz CPU clock

• PCLK1M: 1 MHz peripheral clock

• PCLK16M: 16 MHz peripheral clock

• PCLK32M: 32 MHz peripheral clock

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

• 64 MHz internal oscillator (HFINT)

• 64 MHz crystal oscillator (HFXO)

For illustration, see Clock control on page 62.

When the system requests one or more clocks from the HFCLK controller, the HFCLK controller will

automatically provide them. If the system does not request any clocks provided by the HFCLK controller,

the controller will enter a power saving mode.

These clocks are only available when the system is in ON mode. When the system enters ON mode, the

internal oscillator (HFINT) clock source will automatically start to be able to provide the required HFCLK

clock(s) for the system.

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

triggering the HFCLKSTART task and stopped using the HFCLKSTOP task. A HFCLKSTARTED event will be

generated when the HFXO has started and its frequency is stable.

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

RC oscillator.

5.4.1.1 64 MHz crystal oscillator (HFXO)

The 64 MHz crystal oscillator (HFXO) is controlled by a 32 MHz external crystal

4454_140 v1.0

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