ATmega88 datasheet(147/340 Pages) ATMEL

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7530H–AVR–02/09

ATmega48/88/168 Automotive

Table 15-3 shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to phase cor-

rect PWM mode.

Note:

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

pare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on

page 143 for more details.

• Bits 5:4 – COM2B1:0: Compare Match Output B Mode

These bits control the Output Compare pin (OC2B) behavior. If one or both of the COM2B1:0

bits are set, the OC2B output overrides the normal port functionality of the I/O pin it is connected

to. However, note that the Data Direction Register (DDR) bit corresponding to the OC2B pin

must be set in order to enable the output driver.

When OC2B is connected to the pin, the function of the COM2B1:0 bits depends on the

WGM22:0 bit setting. Table 15-4 shows the COM2B1:0 bit functionality when the WGM22:0 bits

are set to a normal or CTC mode (non-PWM).

Table 15-5 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to fast PWM

mode.

Note:

1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the Com-

pare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on

page 143 for more details.

Table 15-3.

Compare Output Mode, Phase Correct PWM Mode

(1)

COM2A1

COM2A0

Description

Normal port operation, OC2A disconnected.

WGM22 = 0: Normal Port Operation, OC2A Disconnected.

WGM22 = 1: Toggle OC2A on Compare Match.

Clear OC2A on Compare Match when up-counting. Set OC2A on

Compare Match when down-counting.

Set OC2A on Compare Match when up-counting. Clear OC2A on

Compare Match when down-counting.

Table 15-4.

Compare Output Mode, non-PWM Mode

COM2B1

COM2B0

Description

Normal port operation, OC2B disconnected.

Toggle OC2B on Compare Match

Clear OC2B on Compare Match

Set OC2B on Compare Match

Table 15-5.

Compare Output Mode, Fast PWM Mode(1)

COM2B1

COM2B0

Description

Normal port operation, OC2B disconnected.

Reserved

Clear OC2B on Compare Match, set OC2B at TOP

Set OC2B on Compare Match, clear OC2B at TOP

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