Datasheet
158
7593L–AVR–09/12
AT90USB64/128
Table 16-5 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the Com-
pare Match is ignored, but the set or clear is done at TOP. See “Fast PWM mode” on page 151
for more details.
Table 16-6 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to phase cor-
rect PWM mode.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the Com-
pare Match is ignored, but the set or clear is done at TOP. See “Phase correct PWM mode” on
page 153 for more details.
• Bits 3, 2 – Res: Reserved bits
These bits are reserved bits in the Atmel AT90USB64/128 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 wave-
form generation to be used, see Table 16-7. 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 150).
Table 16-5. Compare Output mode, fast PWM mode
(1)
.
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected.
01Reserved
1 0 Clear OC2B on Compare Match, set OC2B at TOP
1 1 Set OC2B on Compare Match, clear OC2B at TOP
Table 16-6. Compare Output mode, phase correct PWM mode
(1)
.
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected
01Reserved
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 16-7. 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)
0 0 0 0 Normal 0xFF Immediate MAX
1 0 0 1 PWM, phase correct 0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF TOP MAX
4100Reserved – – –