AT90USB646_0607 datasheet(113/435 Pages) ATMEL

113 / 435 page

113

7593D–AVR–07/06

AT90USB64/128

• Bits 7:6 – COM01A:0: Compare Match Output A Mode

These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A1:0

bits are set, the OC0A 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 OC0A pin

must be set in order to enable the output driver.

When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the

WGM02:0 bit setting. Table 13-1 shows the COM0A1:0 bit functionality when the WGM02:0 bits

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

Table 13-2 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM

mode.

Note:

1. A special case occurs when OCR0A equals TOP and COM0A1 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 108

for more details.

Table 13-3 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase cor-

rect PWM mode.

Initial Value

Table 13-1.

Compare Output Mode, non-PWM Mode

COM0A1

COM0A0

Description

Normal port operation, OC0A disconnected.

Toggle OC0A on Compare Match

Clear OC0A on Compare Match

Set OC0A on Compare Match

Table 13-2.

Compare Output Mode, Fast PWM Mode

(1)

COM0A1

COM0A0

Description

Normal port operation, OC0A disconnected.

WGM02 = 0: Normal Port Operation, OC0A Disconnected.

WGM02 = 1: Toggle OC0A on Compare Match.

Clear OC0A on Compare Match, set OC0A at TOP

Set OC0A on Compare Match, clear OC0A at TOP

Table 13-3.

Compare Output Mode, Phase Correct PWM Mode

(1)

COM0A1

COM0A0

Description

Normal port operation, OC0A disconnected.

WGM02 = 0: Normal Port Operation, OC0A Disconnected.

WGM02 = 1: Toggle OC0A on Compare Match.

Clear OC0A on Compare Match when up-counting. Set OC0A on

Compare Match when down-counting.

Set OC0A on Compare Match when up-counting. Clear OC0A on

Compare Match when down-counting.

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