ATTINY817-MFR. datasheet(151/492 Pages) MICROCHIP

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where N represents the prescaler divider used.

Dual-slope PWM

For dual-slope 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 for dual-slope PWM the counter counts repeatedly from BOTTOM to TOP

and then from TOP to BOTTOM. The waveform generator output is set on BOTTOM, cleared on compare

match when up-counting, and set on compare match when down-counting.

Figure 20-11. Dual-slope Pulse Width Modulation

MAX

TOP

BOTTOM

CNT

Waveform Output WOn

Period (T)

CMPn=BOTTOM

CMPn=TOP

"update"

"match"

CMPn

Using dual-slope PWM results in a lower maximum operation frequency compared to the single-slope

PWM operation.

The period register (TCA.PER) 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 calculate the exact resolution for dual-slope PWM (RPWM_DS):

��PWM_DS=logPER+1

log2

The PWM frequency depends on the period setting (TCA.PER), the peripheral clock frequency (fCLK_PER),

and the prescaler divider used (CLKSEL in TCA.CTRLA). It is calculated by the following equation:

��PWM_DS=��CLK_PER

2��⋅PER

N represents the prescaler divider used.

Port Override for Waveform Generation

To make the waveform generation available on the Port pins, the corresponding Port pin direction must

be set as output (PORT.DIR[n]=1). The TCA will override the port pin values when the compare channel

is enabled (CMPnEN=1 in TCA.CTRLB) and a waveform generation mode is selected.

The figure below shows the port override for TCA. The timer/counter compare channel will override the

port pin output value (OUT) on the corresponding port pin. Enabling inverted I/O on the port pin

(INVEN=1 in PORT.PINn) inverts the corresponding WG output.

Figure 20-12. Port Override for Timer/Counter Type A

Waveform

OUT

CMPnEN

INVEN

WOn

ATtiny417/817

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ATTINY817-MFR. Datasheet(PDF) 151 Page - Microchip Technology

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