ATmega165 datasheet(132/336 Pages) ATMEL

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132

ATmega165/V

2573G–AVR–07/09

•Bit 5:4 – COM2A1:0: Compare Match Output Mode A

These bits control the Output Compare pin (OC2A) behavior. If one or both of the

COM2A1:0 bits are set, the OC2A output overrides the normal port functionality of the

I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit cor-

responding to OC2A pin must be set in order to enable the output driver.

When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the

WGM21:0 bit setting. Table 55 shows the COM2A1:0 bit functionality when the

WGM21:0 bits are set to a normal or CTC mode (non-PWM).

Table 56 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast

PWM mode.

Note:

1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case,

the compare match is ignored, but the set or clear is done at BOTTOM. See “Fast

PWM Mode” on page 126 for more details.

Table 57 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to

phase correct PWM mode.

Note:

1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case,

the compare match is ignored, but the set or clear is done at TOP. See “Phase Cor-

rect PWM Mode” on page 127 for more details.

• Bit 2:0 – CS22:0: Clock Select

Table 55. Compare Output Mode, non-PWM Mode

COM2A1

COM2A0

Description

Normal port operation, OC2A disconnected.

Toggle OC2A on compare match.

Clear OC2A on compare match.

Set OC2A on compare match.

Table 56. Compare Output Mode, Fast PWM Mode(1)

COM2A1

COM2A0

Description

Normal port operation, OC2A disconnected.

Reserved

Clear OC2A on compare match, set OC2A at BOTTOM,

(non-inverting mode).

Set OC2A on compare match, clear OC2A at BOTTOM,

(inverting mode).

Table 57. Compare Output Mode, Phase Correct PWM Mode

(1)

COM2A1

COM2A0

Description

Normal port operation, OC2A disconnected.

Reserved

Clear OC2A on compare match when up-counting. Set OC2A on

compare match when downcounting.

Set OC2A on compare match when up-counting. Clear OC2A on

compare match when downcounting.

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