ATTINY817-MFR. datasheet(150/492 Pages) MICROCHIP

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Figure 20-9. Frequency Waveform Generation

CNT

WG Output

MAX

TOP

BOTTOM

Period (T)

Direction change

CNT written

"update"

The waveform frequency (fFRQ) is defined by the following equation:

��FRQ= fCLK_PER

2��CMPn+1

where N represents the prescaler divider used (CLKSEL in TCA.CTRLA), and fCLK_PER is the system

clock for the peripherals.

The maximum frequency of the waveform generated is half of the peripheral clock frequency (fCLK_PER/2)

when TCA.CMPn is written to zero (0x0000) and no prescaling is used (N=1, CLKSEL=0x0 in

TCA.CTRLA).

Single-Slope PWM Generation

For single-slope Pulse Width Modulation (PWM) generation, the period (T) is controlled by TCA.PER,

while the values of TCA.CMPn control the duty cycle of the WG output. The figure below shows how the

counter counts from BOTTOM to TOP and then restarts from BOTTOM. The waveform generator (WO)

output is set at TOP, and cleared on the compare match between the TCA.CNT and TCA.CMPn registers.

Figure 20-10. Single-Slope Pulse Width Modulation

CNT

Output WOn

MAX

TOP

CMPn

BOTTOM

Period (T)

CMPn=BOTTOM

CMPn=TOP

"update"

"match"

The TCA.PER register defines the PWM resolution. The minimum resolution is 2 bits

(TCA.PER=0x0003), and the maximum resolution is 16 bits (TCA.PER=MAX).

The following equation calculates the exact resolution for single-slope PWM (RPWM_SS):

��PWM_SS=logPER+1

log2

The single-slope PWM frequency (fPWM_SS) depends on the period setting (TCA_PER), the system's

peripheral clock frequency fCLK_PER, the TCA prescaler (CLKSEL in TCA.CTRLA). It is calculated by the

following equation:

��PWM_SS= ��CLK_PER

��PER+1

ATtiny417/817

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ATTINY817-MFR. Datasheet(PDF) 150 Page - Microchip Technology

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