AT90PWM2 datasheet(99/365 Pages) ATMEL

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4317K–AVR–03/2013

AT90PWM2/3/2B/3B

These bits control the Output Compare pin (OC0B) behavior. If one or both of the COM0B1:0

bits are set, the OC0B output overrides the normal port functionality of the I/O pin it is connected

to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0B pin

must be set in order to enable the output driver.

When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the

WGM02:0 bit setting. Table 14-5 shows the COM0B1:0 bit functionality when the WGM02:0 bits

are set to a normal or CTC mode (non-PWM).

Table 14-6 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM

mode.

Note:

1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Com-

pare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 93

for more details.

Table 14-7 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase cor-

rect PWM mode.

Note:

1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Com-

pare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on

page 95 for more details.

• Bits 3, 2 – Res: Reserved Bits

These bits are reserved bits in the AT90PWM2/2B/3/3B and will always read as zero.

Table 14-5.

Compare Output Mode, non-PWM Mode

COM0B1

COM0B0

Description

Normal port operation, OC0B disconnected.

Toggle OC0B on Compare Match

Clear OC0B on Compare Match

Set OC0B on Compare Match

Table 14-6.

Compare Output Mode, Fast PWM Mode

(1)

COM0B1

COM0B0

Description

Normal port operation, OC0B disconnected.

Reserved

Clear OC0B on Compare Match, set OC0B at TOP

Set OC0B on Compare Match, clear OC0B at TOP

Table 14-7.

Compare Output Mode, Phase Correct PWM Mode

(1)

COM0B1

COM0B0

Description

Normal port operation, OC0B disconnected.

Reserved

Clear OC0B on Compare Match when up-counting. Set OC0B on

Compare Match when down-counting.

Set OC0B on Compare Match when up-counting. Clear OC0B on

Compare Match when down-counting.

AT90PWM2 Datasheet(PDF) 99 Page - ATMEL Corporation

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