ATtiny261-ESSZ datasheet(102/227 Pages) ATMEL

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7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

16.6.1

Compare Output Mode and Waveform Generation

The Waveform Generator uses the COM1x1:0 bits differently in Normal mode and PWM modes.

For all modes, setting the COM1x1:0 = 0 tells the Waveform Generator that no action on the

OCW1x Output is to be performed on the next Compare Match. For compare output actions in

the non-PWM modes refer to Table 16-6 on page 115. For fast PWM mode, refer to Table 16-7

on page 115, and for the Phase and Frequency Correct PWM refer to Table 16-8 on page 116.

A change of the COM1x1:0 bits state will have effect at the first Compare Match after the bits are

written. For non-PWM modes, the action can be forced to have immediate effect by using the

FOC1x strobe bits.

16.7

Modes of Operation

The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is

defined by the combination of the Waveform Generation mode (bits PWM1x and WGM10) and

Compare Output mode (COM1x1:0) bits. The Compare Output mode bits do not affect the

counting sequence, while the Waveform Generation mode bits do. The COM1x1:0 bits control

whether the PWM output generated should be inverted, non-inverted or complementary. For

non-PWM modes the COM1x1:0 bits control whether the output should be set, cleared, or tog-

gled at a Compare Match.

16.7.1

Normal Mode

The simplest mode of operation is the Normal mode (PWM1x = 0), the counter counts from

BOTTOM to TOP (defined as OCR1C) then restarts from BOTTOM. The OCR1C defines the

TOP value for the counter, hence also its resolution, and allows control of the Compare Match

output frequency. In toggle Compare Output Mode the Waveform Output (OCW1x) is toggled at

Compare Match between TCNT1 and OCR1x. In non-inverting Compare Output Mode the

Waveform Output is cleared on the Compare Match. In inverting Compare Output Mode the

Waveform Output is set on Compare Match.

The timing diagram for the Normal mode is shown in Figure 16-10. The counter value (TCNT1)

that is shown as a histogram in the timing diagram is incremented until the counter value

matches the TOP value. The counter is then cleared at the following clock cycle The diagram

includes the Waveform Output (OCW1x) in toggle Compare Mode. The small horizontal line

marks on the TCNT1 slopes represent Compare Matches between OCR1x and TCNT1.

Figure 16-10. Normal Mode, Timing Diagram

TCNTn

OCWnx

(COMnx=1)

OCnx Interrupt Flag Set

Period

TOVn Interrupt Flag Set

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