ATmega162 datasheet(129/324 Pages) ATMEL

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2513K–AVR–07/09

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 PWM

Mode” on page 120. for more details.

Table 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

“Phase Correct PWM Mode” on page 122. for more details.

• 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

(1)

COMnA1/

COMnB1

COMnA0/

COMnB0

Description

Normal port operation, OCnA/OCnB disconnected.

WGMn3:0 = 15: Toggle OCnA on Compare Match, OCnB

disconnected (normal port operation). For all other WGMn

settings, normal port operation, OCnA/OCnB disconnected.

Clear OCnA/OCnB on Compare Match, set OCnA/OCnB at TOP.

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

Normal port operation, OCnA/OCnB disconnected.

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.

Clear OCnA/OCnB on Compare Match when up-counting. Set

OCnA/OCnB on Compare Match when down-counting.

Set OCnA/OCnB on Compare Match when up-counting. Clear

OCnA/OCnB on Compare Match when down-counting.

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