ATMEGA88 datasheet(97/349 Pages) ATMEL

97 / 349 page

ATmega48/88/168

2545D–AVR–07/04

Table 49 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast

PWM mode.

Note:

1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case,

the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM

Mode” on page 91 for more details.

Table 50 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to

phase correct PWM mode.

Note:

1. A special case occurs when OCR0B equals TOP and COM0B1 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 92 for more details.

• Bits 3, 2 – Res: Reserved Bits

These bits are reserved bits in the ATmega48/88/168 and will always read as zero.

• Bits 1:0 – WGM01:0: Waveform Generation Mode

Combined with the WGM02 bit found in the TCCR0B Register, these bits control the

counting sequence of the counter, the source for maximum (TOP) counter value, and

what type of waveform generation to be used, see Table 51. Modes of operation sup-

ported by the Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare

Match (CTC) mode, and two types of Pulse Width Modulation (PWM) modes (see

“Modes of Operation” on page 90).

Table 49. Compare Output Mode, Fast PWM Mode

(1)

COM0B1

COM0B0

Description

Normal port operation, OC0B disconnected.

Reserved

Clear OC0B on Compare Match, set OC0B at TOP

Set OC0B on Compare Match, clear OC0B at TOP

Table 50. Compare Output Mode, Phase Correct PWM Mode(1)

COM0B1

COM0B0

Description

Normal port operation, OC0B disconnected.

Reserved

Clear OC0B on Compare Match when up-counting. Set OC0B on

Compare Match when down-counting.

Set OC0B on Compare Match when up-counting. Clear OC0B on

Compare Match when down-counting.

Table 51. Waveform Generation Mode Bit Description

Mode

WGM02

WGM01

WGM00

Timer/Count

er Mode of

Operation

TOP

Update of

OCRx at

TOV Flag

Set on

(1)(2)

Normal

0xFF

Immediate

MAX

PWM, Phase

Correct

0xFF

TOP

BOTTOM

CTC

OCRA

Immediate

MAX

Fast PWM

0xFF

TOP

MAX

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