NRF52811-QCAA-R datasheet(150/444 Pages) NORDIC

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Peripherals

the COUNTERTOP register. This way one can have up to three PWM channels with a frequency base that

changes on a per PWM period basis. This mode of operation is useful for arbitrary wave form generation

in applications, such as LED lighting.

The register SEQ[n].REFRESH=N (one per sequence n=0 or 1) will instruct a new RAM stored pulse width

value on every (N+1)th PWM period. Setting the register to zero will result in a new duty cycle update

every PWM period, as long as the minimum PWM period is observed.

Note that registers SEQ[n].REFRESH and SEQ[n].ENDDELAY are ignored when DECODER.MODE=NextStep.

The next value is loaded upon every received NEXTSTEP task.

SEQ[n].PTR is the pointer used to fetch COMPARE values from RAM. If the SEQ[n].PTR is not pointing to

a RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See Memory on page

16 for more information about the different memory regions. After the SEQ[n].PTR is set to the desired

RAM location, the SEQ[n].CNT register must be set to number of 16-bit half words in the sequence. It is

important to observe that the Grouped mode requires one half word per group, while the Single mode

requires one half word per channel, thus increasing the RAM size occupation. If PWM generation is not

running when the SEQSTART[n] task is triggered, the task will load the first value from RAM and then start

the PWM generation. A SEQSTARTED[n] event is generated as soon as the EasyDMA has read the first

PWM parameter from RAM and the wave counter has started executing it. When LOOP.CNT=0, sequence

n=0 or 1 is played back once. After the last value in the sequence has been loaded and started executing,

a SEQEND[n] event is generated. The PWM generation will then continue with the last loaded value. The

following figure illustrates an example of such simple playback:

COMPARE

SEQ[0].PTR

COMPARE

SEQ[0].CNT=4, SEQ[0].REFRESH=0, SEQ[0].ENDDELAY=0, LOOP.CNT=0

PWM pulse period

COMPARE

SEQEND[0]

SEQSTARTED[0]

SEQSTART[0]

Event/Tasks

Continues with last setting

Figure 51: Simple sequence example

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