ATmega64A datasheet(159/392 Pages) ATMEL

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159

8160C–AVR–07/09

ATmega64A

Table 17-4 shows the COM21:0 bit functionality when the WGM21:0 bits are set to fast PWM

mode.

Note:

1. A special case occurs when OCR2 equals TOP and COM21 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 152

for more details.

Table 17-5 shows the COM21:0 bit functionality when the WGM21:0 bits are set to phase cor-

rect PWM mode.

Note:

1. A special case occurs when OCR2 equals TOP and COM21 is set. In this case, the Compare

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

154 for more details.

• Bit 2:0 – CS22:0: Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter.

If external pin modes are used for the Timer/Counter2, transitions on the T2 pin will clock the

counter even if the pin is configured as an output. This feature allows software control of the

counting.

Table 17-4.

Compare Output Mode, Fast PWM Mode(1)

COM21

COM20

Description

Normal port operation, OC2 disconnected.

Reserved

Clear OC2 on Compare Match, set OC2 at BOTTOM,

(non-inverting mode).

Set OC2 on Compare Match, clear OC2 at BOTTOM,

(inverting mode).

Table 17-5.

Compare Output Mode, Phase Correct PWM Mode

(1)

COM21

COM20

Description

Normal port operation, OC2 disconnected.

Reserved

Clear OC2 on Compare Match when up-counting. Set OC2 on Compare Match

when downcounting.

Set OC2 on Compare Match when up-counting. Clear OC2 on Compare Match

when downcounting.

Table 17-6.

Clock Select Bit Description

CS22

CS21

CS20

Description

No clock source (Timer/counter stopped).

clkI/O/(No prescaling)

clkI/O/8 (From prescaler)

clkI/O/64 (From prescaler)

clkI/O/256 (From prescaler)

clkI/O/1024 (From prescaler)

External clock source on T2 pin. Clock on falling edge.

External clock source on T2 pin. Clock on rising edge.

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