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2513L–AVR–03/2013
ATmega162/V
Table 54 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the fast PWM
mode.
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. In
this case the Compare Match is ignored, but the set or clear is done at TOP.
See “Fast PWMTable 55 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the phase cor-
rect or the phase and frequency correct, PWM mode.
Note:
1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set.
See Bit 3 – FOCnA: Force Output Compare for channel A
Bit 2 – FOCnB: Force Output Compare for channel B
The FOCnA/FOCnB bits are only active when the WGMn3:0 bits specifies a non-PWM mode.
However, for ensuring compatibility with future devices, these bits must be set to zero when
TCCRnA is written when operating in a PWM mode. When writing a logical one to the
FOCnA/FOCnB bit, an immediate Compare Match is forced on the Waveform Generation unit.
The OCnA/OCnB output is changed according to its COMnx1:0 bits setting. Note that the
FOCnA/FOCnB bits are implemented as strobes. Therefore it is the value present in the
COMnx1:0 bits that determine the effect of the forced compare.
A FOCnA/FOCnB strobe will not generate any interrupt nor will it clear the timer in Clear Timer
on Compare match (CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB bits are always read as zero.
Table 54. Compare Output Mode, Fast PWM
COMnA1/
COMnB1
COMnA0/
COMnB0
Description
0
Normal port operation, OCnA/OCnB disconnected.
0
1
WGMn3:0 = 15: Toggle OCnA on Compare Match, OCnB
disconnected (normal port operation). For all other WGMn
settings, normal port operation, OCnA/OCnB disconnected.
1
0
Clear OCnA/OCnB on Compare Match, set OCnA/OCnB at TOP.
1
Set OCnA/OCnB on Compare Match, clear OCnA/OCnB at TOP.
Table 55. Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM
(1) COMnA1/
COMnB1
COMnA0
COMnB0
Description
0
Normal port operation, OCnA/OCnB disconnected.
0
1
WGMn3:0 = 9 or 14: Toggle OCnA on Compare Match, OCnB
disconnected (normal port operation). For all other WGMn
settings, normal port operation, OCnA/OCnB disconnected.
1
0
Clear OCnA/OCnB on Compare Match when up-counting. Set
OCnA/OCnB on Compare Match when down-counting.
1
Set OCnA/OCnB on Compare Match when up-counting. Clear
OCnA/OCnB on Compare Match when down-counting.