ATmega16 datasheet(75/357 Pages) ATMEL

75 / 357 page

2466S–AVR–05/09

ATmega16(L)

Figure 30. Compare Match Output Unit, Schematic

The general I/O port function is overridden by the Output Compare (OC0) from the Waveform

Generator if either of the COM01:0 bits are set. However, the OC0 pin direction (input or output)

is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Regis-

ter bit for the OC0 pin (DDR_OC0) must be set as output before the OC0 value is visible on the

pin. The port override function is independent of the Waveform Generation mode.

The design of the output compare pin logic allows initialization of the OC0 state before the out-

put is enabled. Note that some COM01:0 bit settings are reserved for certain modes of

operation. See “8-bit Timer/Counter Register Description” on page 83.

Compare Output Mode

and Waveform

Generation

The Waveform Generator uses the COM01:0 bits differently in normal, CTC, and PWM modes.

For all modes, setting the COM01:0 = 0 tells the waveform generator that no action on the OC0

PWM modes refer to Table 39 on page 84. For fast PWM mode, refer to Table 40 on page 84,

and for phase correct PWM refer to Table 41 on page 84.

A change of the COM01:0 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

FOC0 strobe bits.

PORT

DDR

OCn

Waveform

Generator

COMn1

COMn0

FOCn

clk

I/O

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