Data Sheet

107
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
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 Correct PWM Mode” on page 101 for more details.
• Bits 3, 2 – Reserved
These bits are reserved bits in the ATmega48A/PA/88A/PA/168A/PA/328/P 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 15-8. Modes of operation supported 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 99).
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
Table 15-7. Compare Output Mode, Phase Correct PWM Mode
(1)
COM0B1 COM0B0 Description
0 0 Normal port operation, OC0B disconnected.
01Reserved
10
Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.
11
Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.
Table 15-8. Waveform Generation Mode Bit Description
Mode WGM02 WGM01 WGM00
Timer/Counter
Mode of
Operation TOP
Update of
OCRx at
TOV Flag
Set on
(1)(2)
0 0 0 0 Normal 0xFF Immediate MAX
10 0 1
PWM, Phase
Correct
0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF BOTTOM MAX
4 1 0 0 Reserved – – –
51 0 1
PWM, Phase
Correct
OCRA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA BOTTOM TOP