Datasheet

Table Of Contents
184
ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]
2549Q–AVR–02/2014
Table 20-7 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to phase correct PWM mode.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 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 173 for more details.
Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
Bits 1:0 – WGM21:0: Waveform Generation Mode
Combined with the WGM22 bit found in the TCCR2B 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 20-8. 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 171).
Notes: 1. MAX = 0xFF.
2. BOTTOM= 0x00.
Table 20-7. Compare Output Mode, Phase Correct PWM Mode
(1)
COM2B1 COM2B0 Description
00 Normal port operation, OC2B disconnected
01 Reserved
10
Clear OC2B on Compare Match when up-counting
Set OC2B on Compare Match when down-counting
11
Set OC2B on Compare Match when up-counting
Clear OC2B on Compare Match when down-counting
Table 20-8. Waveform Generation Mode Bit Description
Mode WGM2 WGM1 WGM0
Timer/Counter Mode of
Operation TOP
Update of
OCRx at
TOV Flag
Set on
(1)(2)
0000 Normal 0xFF Immediate MAX
1001 PWM, Phase Correct 0xFF TOP BOTTOM
2010 CTC OCRAImmediate MAX
3011 Fast PWM0xFFBOTTOMMAX
4100 Reserved
5101 PWM, Phase Correct OCRA TOP BOTTOM
6110 Reserved
7111 Fast PWM OCRA BOTTOM TOP