Datasheet
121
ATmega325/3250/645/6450
2570K–AVR–04/07
Table 54 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 BOT-
TOM. See “Fast PWM Mode” on page 112. for more details.
Table 55 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 114. 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 56. Modes of operation sup-
ported 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 111.).
Table 54. Compare Output Mode, Fast PWM
(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B
disconnected.
0 1 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.
1 0 Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at BOTTOM (non-inverting mode).
1 1 Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at BOTTOM (inverting mode).
Table 55. 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.
0 1 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.
1 0 Clear OC1A/OC1B on Compare Match when up-
counting. Set OC1A/OC1B on Compare Match
when counting down.
1 1 Set OC1A/OC1B on Compare Match when up-
counting. Clear OC1A/OC1B on Compare Match
when counting down.