
118
4378C–AVR–09/08
AT90PWM1
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set.
See 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 32. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types
Note:
1. The CTCn and PWMn1:0 bit definition names are obsolete. Use the
WGMn2:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
15.10.2
Timer/Counter1 Control Register B – TCCR1B
Bit 7 – ICNCn: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is
activated, the input from the Input Capture pin (ICPn) is filtered. The filter function requires four
successive equal valued samples of the ICPn pin for changing its output. The Input Capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
Bit 6 – ICESn: Input Capture Edge Select
Table 32. Waveform Generation Mode Bit Description
(1) Mode
WGMn3
WGMn2
(CTCn)
WGMn1
(PWMn1)
WGMn0
(PWMn0)
Timer/Counter Mode of
Operation
TOP
Update of
OCRn
x at
TOVn Flag
Set on
0
Normal
0xFFFF
Immediate
MAX
1
0
1
PWM, Phase Correct, 8-bit
0x00FF
TOP
BOTTOM
2
0
1
0
PWM, Phase Correct, 9-bit
0x01FF
TOP
BOTTOM
3
0
1
PWM, Phase Correct, 10-bit
0x03FF
TOP
BOTTOM
4
010
0
CTC
OCRnA
Immediate
MAX
5
0
1
0
1
Fast PWM, 8-bit
0x00FF
TOP
6
0
1
0
Fast PWM, 9-bit
0x01FF
TOP
7
0
1
Fast PWM, 10-bit
0x03FF
TOP
8
100
0
PWM, Phase and Frequency
Correct
ICRn
BOTTOM
9
100
1
PWM, Phase and Frequency
Correct
OCRnA
BOTTOM
10
1
0
1
0
PWM, Phase Correct
ICRn
TOP
BOTTOM
11
1
0
1
PWM, Phase Correct
OCRnA
TOP
BOTTOM
12
1
0
CTC
ICRn
Immediate
MAX
13
1
0
1
(Reserved)
–
14
1
0
Fast PWM
ICRn
TOP
15
1
Fast PWM
OCRnA
TOP
Bit
765
4
3
210
ICNC1
ICES1
–
WGM13
WGM12
CS12
CS11
CS10
TCCR1B
Read/Write
R/W
R
R/W
Initial Value
0