ATtiny261A datasheet(97/292 Pages) ATMEL

97 / 292 page

8197A–AVR–10/09

ATtiny261A/461A/861A

The design of the Output Compare Pin Configuration logic allows initialization of the OC1x state

before the output is enabled. Note that some COM1x1:0 bit settings are reserved for certain

modes of operation. For Output Compare Pin Configurations refer to Table 12-2 on page 98,

Table 12-3 on page 100, Table 12-4 on page 102, Table 12-5 on page 103, Table 12-6 on page

103, and Table 12-7 on page 104.

12.7.1

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 12-8 on page 110. For fast PWM mode, refer to Table 12-9

on page 110, and for the Phase and Frequency Correct PWM refer to Table 12-10 on page 111.

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.

12.8 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 waveform generation mode bits (PWM1A, PWM1B, and

WGM11:10) and compare output mode bits (COM1x1:0). 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

toggled at a Compare Match.

12.8.1

Normal Mode

The simplest mode of operation is Normal mode (PWM1A/PWM1B = 0), where 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 Com-

pare 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 Normal mode is

shown in Figure 12-11.

Figure 12-11. Normal Mode, Timing Diagram

TCNTn

OCWnx

(COMnx=1)

OCnx Interrupt Flag Set

Period

TOVn Interrupt Flag Set

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