CLOCK — Clock control

The clock control system can source the system clocks from a range of internal or external high and low frequency oscillators and distribute them to modules based upon a module’s individual requirements. Clock distribution is automated and grouped independently by module to limit current consumption in unused branches of the clock tree.

Listed here are the main features for CLOCK:

64 MHz on-chip oscillator
64 MHz crystal oscillator, using external 32 MHz crystal
32.768 kHz +/-500 ppm RC oscillator
32.768 kHz crystal oscillator, using external 32.768 kHz crystal
32.768 kHz oscillator synthesized from 64 MHz oscillator
Firmware (FW) override control of crystal oscillator activity for low latency start up
Automatic internal oscillator and clock control, and distribution for ultra-low power

Figure 1. Clock control

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.

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).
HFXO debounce time, as specified in register HFXODEBOUNCE.

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

64 MHz crystal oscillator (HFXO)

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

The crystal oscillator is designed for use with an AT-cut quartz crystal in parallel resonant mode. To achieve correct oscillation frequency, the load capacitance must match the specification in the crystal data sheet.

Circuit diagram of the 64 MHz crystal oscillator shows how the 32 MHz crystal is connected to the 64 MHz crystal oscillator.

Figure 2. Circuit diagram of the 64 MHz crystal oscillator

The load capacitance (CL) is the total capacitance seen by the crystal across its terminals and is given by:

C1 and C2 are ceramic SMD capacitors connected between each crystal terminal and ground. For more information, see Reference circuitry. C_pcb1 and C_pcb2 are stray capacitances on the PCB. C_pin is the pin input capacitance on the XC1 and XC2 pins. See table 64 MHz crystal oscillator (HFXO). The load capacitors C1 and C2 should have the same value.

For reliable operation, the crystal load capacitance, shunt capacitance, equivalent series resistance, and drive level must comply with the specifications in table 64 MHz crystal oscillator (HFXO). It is recommended to use a crystal with lower than maximum load capacitance and/or shunt capacitance. A low load capacitance will reduce both start up time and current consumption.

LFCLK controller

The system supports several low frequency clock sources.

As illustrated in Clock control, the system supports the following low frequency clock sources:

32.768 kHz RC oscillator (LFRC)
32.768 kHz crystal oscillator (LFXO)
32.768 kHz synthesized from HFCLK (LFSYNT)

The LFCLK controller and all of the LFCLK clock sources are always switched off when in System OFF mode.

The LFCLK clock is started by first selecting the preferred clock source in register LFCLKSRC and then triggering the LFCLKSTART task. If the LFXO is selected as the clock source, the LFCLK will initially start running from the 32.768 kHz LFRC while the LFXO is starting up and automatically switch to using the LFXO once this oscillator is running. The LFCLKSTARTED event will be generated when the LFXO has been started.

The register LFXODEBOUNCE is used to configure the LFXO debounce time. The register must be modified if operating in the Extended Operating Conditions temperature range, see Recommended operating conditions. The LFXO start up time will be increased as a result.

The LFCLK clock is stopped by triggering the LFCLKSTOP task.

Register LFCLKSRC controls the clock source, and its allowed swing. The truth table for various situations is as follows:

Table 1. LFCLKSRC configuration depending on clock source
SRC	EXTERNAL	BYPASS	Comment
0	0	0	Normal operation, LFRC is source
0	0	1	DO NOT USE
0	1	X	DO NOT USE
1	0	0	Normal XTAL operation
1	1	0	Apply external low swing signal to XL1, ground XL2
1	1	1	Apply external full swing signal to XL1, leave XL2 grounded or unconnected
1	0	1	DO NOT USE
2	0	0	Normal operation, LFSYNT is source
2	0	1	DO NOT USE
2	1	X	DO NOT USE

It is not allowed to write to register LFCLKSRC when the LFCLK is running.

A LFCLKSTOP task will stop the LFCLK oscillator. However, the LFCLKSTOP task can only be triggered after the STATE field in register LFCLKSTAT indicates LFCLK running state.

The synthesized 32.768 kHz clock depends on the HFCLK to run. If high accuracy is required for the LFCLK running off the synthesized 32.768 kHz clock, the HFCLK must running from the HFXO source.

32.768 kHz RC oscillator (LFRC)

The default source of the low frequency clock (LFCLK) is the 32.768 kHz RC oscillator (LFRC).

The LFRC oscillator does not require additional external components.

The LFRC frequency will be affected by variation in temperature. The LFRC oscillator can be calibrated to improve accuracy by using the HFXO as a reference oscillator during calibration.

Calibrating the 32.768 kHz RC oscillator

After the LFRC oscillator is started and running, it can be calibrated by triggering the CAL task.

The LFRC oscillator will then temporarily request the HFCLK to be used as a reference for the calibration. A DONE event will be generated when calibration has finished. The HFCLK crystal oscillator has to be started (by triggering the HFCLKSTART task) in order for the calibration mechanism to work.

It is not allowed to stop the LFRC during an ongoing calibration.

Calibration timer

The calibration timer can be used to time the calibration interval of the 32.768 kHz RC oscillator.

The calibration timer is started by triggering the CTSTART task and stopped by triggering the CTSTOP task. The calibration timer will always start counting down from the value specified in CTIV (Retained) and generate a CTTO event when it reaches 0. The calibration timer will automatically stop when it reaches 0.

Figure 3. Calibration timer

After a CTSTART task has been triggered, the calibration timer will ignore further tasks until it has returned the CTSTARTED event. Likewise, after a CTSTOP task has been triggered, the calibration timer will ignore further tasks until it has returned a CTSTOPPED event. Triggering CTSTART while the calibration timer is running will immediately return a CTSTARTED event. Triggering CTSTOP when the calibration timer is stopped will immediately return a CTSTOPPED event.

32.768 kHz crystal oscillator (LFXO)

For higher LFCLK accuracy (when better than +/- 500 ppm accuracy is required), the low frequency crystal oscillator (LFXO) must be used.

The following external clock sources are supported:

Low swing clock signal applied to the XL1 pin. The XL2 pin shall then be grounded.
Rail-to-rail clock signal applied to the XL1 pin. The XL2 pin shall then be grounded or left unconnected.

To achieve correct oscillation frequency, the load capacitance must match the specification in the crystal data sheet. Circuit diagram of the 32.768 kHz crystal oscillator shows the LFXO circuitry.

Figure 4. Circuit diagram of the 32.768 kHz crystal oscillator

The load capacitance (CL) is the total capacitance seen by the crystal across its terminals and is given by:

C1 and C2 are ceramic SMD capacitors connected between each crystal terminal and ground. C_pcb1 and C_pcb2 are stray capacitances on the PCB. C_pin is the pin input capacitance on the XC1 and XC2 pins (see Low frequency crystal oscillator (LFXO)). The load capacitors C1 and C2 should have the same value.

For more information, see Reference circuitry.

32.768 kHz synthesized from HFCLK (LFSYNT)

LFCLK can also be synthesized from the HFCLK clock source. The accuracy of LFCLK will then be the accuracy of the HFCLK.

Using the LFSYNT clock avoids the requirement for a 32.768 kHz crystal, but increases average power consumption as the HFCLK will need to be requested in the system.

Registers

Instances


Instance	Base address	Description
CLOCK	0x40000000	Clock control

Register overview


Register	Offset	Description
TASKS_HFCLKSTART	0x000	Start HFXO crystal oscillator
TASKS_HFCLKSTOP	0x004	Stop HFXO crystal oscillator
TASKS_LFCLKSTART	0x008	Start LFCLK
TASKS_LFCLKSTOP	0x00C	Stop LFCLK
TASKS_CAL	0x010	Start calibration of LFRC
TASKS_CTSTART	0x014	Start calibration timer
TASKS_CTSTOP	0x018	Stop calibration timer
EVENTS_HFCLKSTARTED	0x100	HFXO crystal oscillator started
EVENTS_LFCLKSTARTED	0x104	LFCLK started
EVENTS_DONE	0x10C	Calibration of LFRC completed
EVENTS_CTTO	0x110	Calibration timer timeout
EVENTS_CTSTARTED	0x128	Calibration timer has been started and is ready to process new tasks
EVENTS_CTSTOPPED	0x12C	Calibration timer has been stopped and is ready to process new tasks
INTENSET	0x304	Enable interrupt
INTENCLR	0x308	Disable interrupt
HFCLKRUN	0x408	Status indicating that HFCLKSTART task has been triggered
HFCLKSTAT	0x40C	HFCLK status
LFCLKRUN	0x414	Status indicating that LFCLKSTART task has been triggered
LFCLKSTAT	0x418	LFCLK status
LFCLKSRCCOPY	0x41C	Copy of LFCLKSRC register, set when LFCLKSTART task was triggered
LFCLKSRC	0x518	Clock source for the LFCLK
HFXODEBOUNCE	0x528	HFXO debounce time. The HFXO is started by triggering the TASKS_HFCLKSTART task.
LFXODEBOUNCE	0x52C	LFXO debounce time. The LFXO is started by triggering the TASKS_LFCLKSTART task when the LFCLKSRC register is configured for Xtal.
CTIV	0x538	Calibration timer interval This register is retained.
TRACECONFIG	0x55C	Clocking options for the trace port debug interface

TASKS_HFCLKSTART

Address offset: 0x000

Start HFXO crystal oscillator


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_HFCLKSTART										Start HFXO crystal oscillator
			Trigger	1								Trigger task

TASKS_HFCLKSTOP

Address offset: 0x004

Stop HFXO crystal oscillator


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_HFCLKSTOP										Stop HFXO crystal oscillator
			Trigger	1								Trigger task

TASKS_LFCLKSTART

Address offset: 0x008

Start LFCLK


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_LFCLKSTART										Start LFCLK
			Trigger	1								Trigger task

TASKS_LFCLKSTOP

Address offset: 0x00C

Stop LFCLK


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_LFCLKSTOP										Stop LFCLK
			Trigger	1								Trigger task

TASKS_CAL

Address offset: 0x010

Start calibration of LFRC


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_CAL										Start calibration of LFRC
			Trigger	1								Trigger task

TASKS_CTSTART

Address offset: 0x014

Start calibration timer


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_CTSTART										Start calibration timer
			Trigger	1								Trigger task

TASKS_CTSTOP

Address offset: 0x018

Stop calibration timer


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	TASKS_CTSTOP										Stop calibration timer
			Trigger	1								Trigger task

EVENTS_HFCLKSTARTED

Address offset: 0x100

HFXO crystal oscillator started


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_HFCLKSTARTED										HFXO crystal oscillator started
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_LFCLKSTARTED

Address offset: 0x104

LFCLK started


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_LFCLKSTARTED										LFCLK started
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_DONE

Address offset: 0x10C

Calibration of LFRC completed


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_DONE										Calibration of LFRC completed
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_CTTO

Address offset: 0x110

Calibration timer timeout


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_CTTO										Calibration timer timeout
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_CTSTARTED

Address offset: 0x128

Calibration timer has been started and is ready to process new tasks


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_CTSTARTED										Calibration timer has been started and is ready to process new tasks
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_CTSTOPPED

Address offset: 0x12C

Calibration timer has been stopped and is ready to process new tasks


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	EVENTS_CTSTOPPED										Calibration timer has been stopped and is ready to process new tasks
			NotGenerated	0								Event not generated
			Generated	1								Event generated

INTENSET

Address offset: 0x304

Enable interrupt


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																								F	E						D	C		B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	HFCLKSTARTED										Write '1' to enable interrupt for event HFCLKSTARTED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	LFCLKSTARTED										Write '1' to enable interrupt for event LFCLKSTARTED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	DONE										Write '1' to enable interrupt for event DONE
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	CTTO										Write '1' to enable interrupt for event CTTO
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
E	RW	CTSTARTED										Write '1' to enable interrupt for event CTSTARTED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
F	RW	CTSTOPPED										Write '1' to enable interrupt for event CTSTOPPED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																								F	E						D	C		B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	HFCLKSTARTED										Write '1' to disable interrupt for event HFCLKSTARTED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	LFCLKSTARTED										Write '1' to disable interrupt for event LFCLKSTARTED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	DONE										Write '1' to disable interrupt for event DONE
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	CTTO										Write '1' to disable interrupt for event CTTO
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
E	RW	CTSTARTED										Write '1' to disable interrupt for event CTSTARTED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
F	RW	CTSTOPPED										Write '1' to disable interrupt for event CTSTOPPED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

HFCLKRUN

Address offset: 0x408

Status indicating that HFCLKSTART task has been triggered


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	STATUS										HFCLKSTART task triggered or not
			NotTriggered	0								Task not triggered
			Triggered	1								Task triggered

HFCLKSTAT

Address offset: 0x40C

HFCLK status


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																			B																A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	SRC										Source of HFCLK
			RC	0								64 MHz internal oscillator (HFINT)
			Xtal	1								64 MHz crystal oscillator (HFXO)
B	R	STATE										HFCLK state
			NotRunning	0								HFCLK not running
			Running	1								HFCLK running

LFCLKRUN

Address offset: 0x414

Status indicating that LFCLKSTART task has been triggered


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	STATUS										LFCLKSTART task triggered or not
			NotTriggered	0								Task not triggered
			Triggered	1								Task triggered

LFCLKSTAT

Address offset: 0x418

LFCLK status


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																			B															A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	SRC										Source of LFCLK
			RC	0								32.768 kHz RC oscillator (LFRC)
			Xtal	1								32.768 kHz crystal oscillator (LFXO)
			Synth	2								32.768 kHz synthesized from HFCLK (LFSYNT)
B	R	STATE										LFCLK state
			NotRunning	0								LFCLK not running
			Running	1								LFCLK running

LFCLKSRCCOPY

Address offset: 0x41C

Copy of LFCLKSRC register, set when LFCLKSTART task was triggered


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																		A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	SRC										Clock source
			RC	0								32.768 kHz RC oscillator (LFRC)
			Xtal	1								32.768 kHz crystal oscillator (LFXO)
			Synth	2								32.768 kHz synthesized from HFCLK (LFSYNT)

LFCLKSRC

Address offset: 0x518

Clock source for the LFCLK


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																		C	B															A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	SRC										Clock source
			RC	0								32.768 kHz RC oscillator (LFRC)
			Xtal	1								32.768 kHz crystal oscillator (LFXO)
			Synth	2								32.768 kHz synthesized from HFCLK (LFSYNT)
B	RW	BYPASS										Enable or disable bypass of LFCLK crystal oscillator with external clock source
			Disabled	0								Disable (use with Xtal or low-swing external source)
			Enabled	1								Enable (use with rail-to-rail external source)
C	RW	EXTERNAL										Enable or disable external source for LFCLK
			Disabled	0								Disable external source (use with Xtal)
			Enabled	1								Enable use of external source instead of Xtal (SRC needs to be set to Xtal)

HFXODEBOUNCE

Address offset: 0x528

HFXO debounce time. The HFXO is started by triggering the TASKS_HFCLKSTART task.

The EVENTS_HFCLKSTARTED event is generated after the HFXO power up time + the HFXO debounce time has elapsed. It is not allowed to change the value of this register while the HFXO is starting.


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																												A	A	A	A	A	A	A	A
Reset 0x00000010				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	HFXODEBOUNCE		0x01..0xFF								HFXO debounce time. Debounce time = HFXODEBOUNCE * 16 µs.
			Db256us	0x10								256 µs debounce time. Recommended for 1.6 mm x 2.0 mm crystals and larger.
			Db1024us	0x40								1024 µs debounce time. Recommended for 1.6 mm x 1.2 mm crystals and smaller.

LFXODEBOUNCE

Address offset: 0x52C

LFXO debounce time. The LFXO is started by triggering the TASKS_LFCLKSTART task when the LFCLKSRC register is configured for Xtal.

The EVENTS_LFCLKSTARTED event is generated after the LFXO debounce time has elapsed. It is not allowed to change the value of this register while the LFXO is starting.


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	LFXODEBOUNCE										LFXO debounce time.
			Normal	0								8192 32.768 kHz periods, or 0.25 s. Recommended for normal Operating Temperature conditions.
			Extended	1								16384 32.768 kHz periods, or 0.5 s. Recommended for Extended Operating Temperature conditions.

CTIV (Retained)

Address offset: 0x538

Calibration timer interval

This register is retained.


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																													A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	CTIV										Calibration timer interval in multiple of 0.25 seconds. Range: 0.25 seconds to 31.75 seconds.

TRACECONFIG

Address offset: 0x55C

Clocking options for the trace port debug interface

This register is a retained register. Reset behavior is the same as debug components.


Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																		B	B															A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	TRACEPORTSPEED										Speed of trace port clock. Note that the TRACECLK pin will output this clock divided by two.
			32MHz	0								32 MHz trace port clock (TRACECLK = 16 MHz)
			16MHz	1								16 MHz trace port clock (TRACECLK = 8 MHz)
			8MHz	2								8 MHz trace port clock (TRACECLK = 4 MHz)
			4MHz	3								4 MHz trace port clock (TRACECLK = 2 MHz)
B	RW	TRACEMUX										Pin multiplexing of trace signals. See pin assignment chapter for more details.
			GPIO	0								No trace signals routed to pins. All pins can be used as regular GPIOs.
			Serial	1								SWO trace signal routed to pin. Remaining pins can be used as regular GPIOs.
			Parallel	2								All trace signals (TRACECLK and TRACEDATA[n]) routed to pins.

Electrical specification

64 MHz internal oscillator (HFINT)


Symbol	Description	Typ.	Max.	Units
f_{NOM_HFINT}	Nominal output frequency	64		MHz
f_{TOL_HFINT}	Frequency tolerance	±1.5	±8	%
f_{TOL_HFINT,EXT}	Frequency tolerance, extended temperature range		±9	%

64 MHz crystal oscillator (HFXO)


Symbol	Description	Typ.	Max.	Units
f_{NOM_HFXO}	Nominal output frequency	64		MHz
f_{XTAL_HFXO}	External crystal frequency	32		MHz
f_{TOL_HFXO}	Frequency tolerance requirement for 2.4 GHz proprietary radio applications		±60	ppm
f_{TOL_HFXO_BLE}	Frequency tolerance requirement, Bluetooth low energy applications, packet length ≤ 200 bytes		±40	ppm
f_{TOL_HFXO_BLE_LP}	Frequency tolerance requirement, Bluetooth low energy applications, packet length > 200 bytes		±30	ppm
C_{L_HFXO}	Load capacitance		12	pF
C_{0_HFXO}	Shunt capacitance		7	pF
R_{S_HFXO_7PF}	Equivalent series resistance 3 pF < C0 ≤ 7 pF		60	Ω
R_{S_HFXO_3PF}	Equivalent series resistance C0 ≤ 3 pF		100	Ω
P_{D_HFXO}	Drive level		100	µW
C_{PIN_HFXO}	Input capacitance XC1 and XC2	3		pF
I_{STBY_X32M}	Core standby current for various crystals
I_{STBY_X32M_X0}	Typical parameters for a given 2.5mm x 2.0mm crystal: CL_HFXO = 8 pF, C0_HFXO = 1 pF, LM_HFXO = 7 mH, RS_HFXO = 20 Ω	65		µA
I_{STBY_X32M_X1}	Typical parameters for a given 1.6mm x 1.2mm crystal: CL_HFXO = 8 pF, C0_HFXO = 0.4 pF, LM_HFXO = 20 mH, RS_HFXO = 40 Ω	110		µA
I_{START_X32M}	Average startup current for various crystals, first 1 ms
I_{START_X32M_X0}	Typical parameters for a given 2.5mm x 2.0mm crystal: CL_HFXO = 8 pF, C0_HFXO = 1 pF, LM_HFXO = 7 mH, RS_HFXO = 20 Ω	360		µA
I_{START_X32M_X1}	Typical parameters for a given 1.6mm x 1.2mm crystal: CL_HFXO = 8 pF, C0_HFXO = 0.4 pF, LM_HFXO = 20 mH, RS_HFXO = 40 Ω	785		µA
t_{POWERUP_X32M}	Power-up time for various crystals
t_{POWERUP_X32M_X0}	Typical parameters for a given 2.5mm x 2.0mm crystal: CL_HFXO = 8 pF, C0_HFXO = 1 pF, LM_HFXO = 7 mH, RS_HFXO = 20 Ω	60		µs
t_{POWERUP_X32M_X1}	Typical parameters for a given 1.6mm x 1.2mm crystal: CL_HFXO = 8 pF, C0_HFXO = 0.4 pF, LM_HFXO = 20 mH, RS_HFXO = 40 Ω	200		µs

Low frequency crystal oscillator (LFXO)


Symbol	Description	Min.	Typ.	Max.	Units
f_{NOM_LFXO}	Crystal frequency		32.768		kHz
f_{TOL_LFXO_BLE}	Frequency tolerance requirement for BLE stack			±500	ppm
f_{TOL_LFXO_ANT}	Frequency tolerance requirement for ANT stack			±50	ppm
C_{L_LFXO}	Load capacitance			12.5	pF
C_{0_LFXO}	Shunt capacitance			2	pF
R_{S_LFXO}	Equivalent series resistance			100	kΩ
P_{D_LFXO}	Drive level			0.5	μW
C_pin	Input capacitance on XL1 and XL2 pads		4		pF
I_LFXO	Run current for 32.768 kHz crystal oscillator		0.23		µA
t_{START_LFXO}	Startup time for 32.768 kHz crystal oscillator		0.25		s
t_{START_LFXO_EXT}	Startup time for 32.768 kHz crystal oscillator when CLOCK.LFXODEBOUNCE configured for Extended debounce time		0.5		s
V_{AMP,IN,XO,LOW}	Peak to peak amplitude for external low swing clock. Input signal must not swing outside supply rails.	200		1000	mV

Low frequency RC oscillator (LFRC)


Symbol	Description	Typ.	Max.	Units
f_{NOM_LFRC}	Nominal frequency	32.768		kHz
f_{TOL_LFRC}	Frequency tolerance, uncalibrated		±5	%
f_{TOL_CAL_LFRC}	Frequency tolerance after calibration¹		±500	ppm
I_LFRC	Run current	0.7		µA
t_{START_LFRC}	Startup time	1000		μs

Synthesized low frequency clock (LFSYNT)


Symbol	Description	Min.	Typ.	Max.	Units
f_{NOM_LFSYNT}	Nominal frequency		32.768		kHz

¹ Constant temperature within ±0.5 °C, calibration performed at least every 8 seconds, averaging interval > 7.5 ms, defined as 3 sigma