ATmega64A datasheet(158/392 Pages) ATMEL

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158

8160C–AVR–07/09

ATmega64A

A FOC2 strobe will not generate any interrupt, nor will it clear the timer in CTC mode using

OCR2 as TOP.

The FOC2 bit is always read as zero.

• Bit 6, 3 – WGM21:0: Waveform Generation Mode

These bits control the counting sequence of the counter, the source for the maximum (TOP)

counter value, and what type of waveform generation to be used. Modes of operation supported

by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and

two types of Pulse Width Modulation (PWM) modes. See Table 17-2 and “Modes of Operation”

on page 151.

Note:

1. The CTC2 and PWM2 bit definition names are now obsolete. Use the WGM21:0 definitions.

However, the functionality and location of these bits are compatible with previous versions of

the timer.

• Bit 5:4 – COM21:0: Compare Match Output Mode

These bits control the Output Compare pin (OC2) behavior. If one or both of the COM21:0 bits

are set, the OC2 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 OC2 pin must be

set in order to enable the output driver.

When OC2 is connected to the pin, the function of the COM21:0 bits depends on the WGM21:0

bit setting. Table 17-3 shows the COM21:0 bit functionality when the WGM21:0 bits are set to a

Normal or CTC mode (non-PWM).

Table 17-2.

Waveform Generation Mode Bit Description(1)

Mode

WGM21

(CTC2)

WGM20

(PWM2)

Timer/Counter Mode of

Operation

TOP

Update of

OCR2

TOV2 Flag

Set on

Normal

0xFF

Immediate

MAX

PWM, Phase Correct

0xFF

TOP

BOTTOM

CTC

OCR2

Immediate

MAX

Fast PWM

0xFF

BOTTOM

MAX

Table 17-3.

Compare Output Mode, non-PWM Mode

COM21

COM20

Description

Normal port operation, OC2 disconnected.

Toggle OC2 on Compare Match.

Clear OC2 on Compare Match.

Set OC2 on Compare Match.

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