137
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
Table 16-2 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast
PWM mode.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In
this case the compare match is ignored, but the set or clear is done at BOTTOM. See ”Fast
PWM Mode” on page 128 for more details.
Table 16-3 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the phase
correct or the phase and frequency correct, PWM mode.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. See
”Phase Correct PWM Mode” on page 130 for more details.
• Bit 1:0 – WGM11:0: Waveform Generation Mode
Combined with the WGM13:2 bits found in the TCCR1B 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 16-4. 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 ”Modes of Operation” on page 127).
Table 16-2. Compare Output Mode, Fast PWM
(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
01
WGM13:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port operation).
For all other WGM1 settings, normal port operation,
OC1A/OC1B disconnected.
10
Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at BOTTOM (non-inverting mode)
11
Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at BOTTOM (inverting mode)
Table 16-3. Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM
(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
01
WGM13:0 = 9 or 11: Toggle OC1A on Compare
Match, OC1B disconnected (normal port operation).
For all other WGM1 settings, normal port operation,
OC1A/OC1B disconnected.
10
Clear OC1A/OC1B on Compare Match when up-
counting. Set OC1A/OC1B on Compare Match when
downcounting.
11
Set OC1A/OC1B on Compare Match when up-
counting. Clear OC1A/OC1B on Compare Match
when downcounting.
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