Table 15-4. Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
COMnA1/COMnB1
COMnA0/COMnB0
Description
WGMn3:0 = 8, 9 10 or 11: Toggle OCnA on Compare
Match, OCnB disconnected (normal port operation).
For all other WGM1 settings, normal port operation,
OC1A/OC1B disconnected.
0
1
Clear OCnA/OCnB on Compare Match when up-
counting. Set OCnA/OCnB on Compare Match when
downcounting.
1
1
0
1
Set OCnA/OCnB on Compare Match when up-
counting. Clear OCnA/OCnB on Compare Match
when downcounting.
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. See
“Phase Correct PWM Mode” on page 117. for more details.
• Bit 1:0 – WGMn1:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB 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 15-5. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types
of Pulse Width Modulation (PWM) modes. (See “16-bit Timer/Counter1 with PWM” on page
102.).
Table 15-5. Waveform Generation Mode Bit Description(1)
WGMn2
(CTCn)
WGMn1
WGMn0
Timer/Counter Mode of
Update of
OCRnx at
TOVn Flag
Set on
Mode
WGMn3
(PWMn1) (PWMn0) Operation
TOP
0
1
2
3
4
5
6
7
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Normal
0xFFFF
0x00FF
0x01FF
0x03FF
OCRnA
0x00FF
0x01FF
0x03FF
Immediate
TOP
MAX
PWM, Phase Correct, 8-bit
PWM, Phase Correct, 9-bit
PWM, Phase Correct, 10-bit
CTC
BOTTOM
BOTTOM
BOTTOM
MAX
TOP
TOP
Immediate
TOP
Fast PWM, 8-bit
TOP
Fast PWM, 9-bit
TOP
TOP
Fast PWM, 10-bit
TOP
TOP
PWM, Phase and Frequency
Correct
8
9
1
1
0
0
0
0
0
1
ICRn
BOTTOM
BOTTOM
BOTTOM
BOTTOM
PWM, Phase and Frequency
Correct
OCRnA
10
11
12
13
14
15
1
1
1
1
1
1
0
0
1
1
1
1
1
1
0
0
1
1
0
1
0
1
0
1
PWM, Phase Correct
PWM, Phase Correct
CTC
ICRn
OCRnA
ICRn
–
TOP
TOP
Immediate
–
BOTTOM
BOTTOM
MAX
(Reserved)
–
Fast PWM
ICRn
OCRnA
TOP
TOP
TOP
Fast PWM
TOP
124
AT90PWM2/3/2B/3B
4317J–AVR–08/10
ATMEL [ ATMEL ]
