Table 45. Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1
COM1A0/COM1B0
Description
0
0
Normal port operation, OC1A/OC1B
disconnected.
0
1
WGM13:0 = 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation).
For all other WGM13:0 settings, normal port
operation, OC1A/OC1B disconnected.
1
1
0
1
Clear OC1A/OC1B on compare match, set
OC1A/OC1B at BOTTOM,
(non-inverting mode)
Set OC1A/OC1B on compare match, clear
OC1A/OC1B at BOTTOM,
(inverting 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 99. for more details.
Table 46 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.
Table 46. 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 14: Toggle OC1A on
Compare Match, OC1B disconnected (normal
port operation).
For all other WGM13:0 settings, normal port
operation, OC1A/OC1B disconnected.
1
1
0
1
Clear OC1A/OC1B on compare match when
up-counting. Set OC1A/OC1B on compare
match when downcounting.
Set OC1A/OC1B on compare match when up-
counting. Clear OC1A/OC1B on compare
match when downcounting.
Note:
1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is
set. See “Phase Correct PWM Mode” on page 101. for more details.
• Bit 3 – FOC1A: Force Output Compare for Compare unit A
• Bit 2 – FOC1B: Force Output Compare for Compare unit B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM
mode. However, for ensuring compatibility with future devices, these bits must be set to
zero when TCCR1A is written when operating in a PWM mode. When writing a logical
one to the FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform
Generation unit. The OC1A/OC1B output is changed according to its COM1x1:0 bits
setting. Note that the FOC1A/FOC1B bits are implemented as strobes. Therefore it is
the value present in the COM1x1:0 bits that determine the effect of the forced compare.
108
ATmega32(L)
2503J–AVR–10/06
ATMEL [ ATMEL ]
