User Manual

133
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
8271E–AVR–07/2012
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 126 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 waveform 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 Opera-
tion” on page 123).
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.
Table 16-4. Waveform Generation Mode Bit Description
(1)
Mode WGM13
WGM12
(CTC1)
WGM11
(PWM11)
WGM10
(PWM10)
Timer/Counter Mode of
Operation TOP
Update of
OCR1x at
TOV1 Flag
Set on
0 0 0 0 0 Normal 0xFFFF Immediate MAX
1 0 0 0 1 PWM, Phase Correct, 8-bit 0x00FF TOP BOTTOM
2 0 0 1 0 PWM, Phase Correct, 9-bit 0x01FF TOP BOTTOM
3 0 0 1 1 PWM, Phase Correct, 10-bit 0x03FF TOP BOTTOM
4 0 1 0 0 CTC OCR1A Immediate MAX
5 0 1 0 1 Fast PWM, 8-bit 0x00FF BOTTOM TOP
6 0 1 1 0 Fast PWM, 9-bit 0x01FF BOTTOM TOP
7 0 1 1 1 Fast PWM, 10-bit 0x03FF BOTTOM TOP
81000
PWM, Phase and Frequency
Correct
ICR1 BOTTOM BOTTOM
91001
PWM, Phase and Frequency
Correct
OCR1A BOTTOM BOTTOM
10 1 0 1 0 PWM, Phase Correct ICR1 TOP BOTTOM
11 1 0 1 1 PWM, Phase Correct OCR1A TOP BOTTOM
12 1 1 0 0 CTC ICR1 Immediate MAX