ATtiny167-ESSZ datasheet(122/282 Pages) ATMEL

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7728D–AVR–07/09

ATtiny87/ATtiny167

Figure 12-6. Compare Match Output Logic

12.8.1

Compare Output Function

The general I/O port function is overridden by the Output Compare (OC1A/B) from the Wave-

form Generator if either of the COM1A/B1:0 bits are set and if OCnxi respective bit is set in

TCCR1D register. However, the OC1A/Bi pin direction (input or output) is still controlled by the

Data Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC1A/Bi

pin (DDR_OC1A/Bi) must be set as output before the OC1A/B value is visible on the pin. The

port override function is generally independent of the Waveform Generation mode, but there

are some exceptions. Refer to Table 12-1, Table 12-2 and Table 12-3 for details.

The design of the Output Compare pin logic allows initialization of the OC1A/B state before the

output is enabled. Note that some COM1A/B1:0 bit settings are reserved for certain modes of

operation. See “16-bit Timer/Counter Register Description” on page 132.

The COM1A/B1:0 bits have no effect on the Input Capture unit.

12.8.2

Compare Output Mode and Waveform Generation

The Waveform Generator uses the COM1A/B1:0 bits differently in normal, CTC, and PWM

modes. For all modes, setting the COM1A/B1:0 = 0 tells the Waveform Generator that no

action on the OC1A/B Register is to be performed on the next compare match. For compare

output actions in the non-PWM modes refer to Table 12-1 on page 132. For fast PWM mode

refer to Table 12-2 on page 133, and for phase correct and phase and frequency correct PWM

refer to Table 12-3 on page 133.

A change of the COM1A/B1:0 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 FOC1A/B strobe bits.

12.9

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 (WGM13:0) and Compare

Output mode (COM1A/B1:0) bits. The Compare Output mode bits do not affect the counting

sequence, while the Waveform Generation mode bits do. The COM1A/B1:0 bits control

whether the PWM output generated should be inverted or not (inverted or non-inverted PWM).

For non-PWM modes the COM1A/B1:0 bits control whether the output should be set, cleared

PORT

OCnxi

OCnx

Waveform

Generator

COMnx1

OCnxi

COMnx0

FOCnx

clk

I/O

DDR

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