ATmega88 datasheet(149/340 Pages) ATMEL

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7530H–AVR–02/09

ATmega48/88/168 Automotive

15.8.2

Timer/Counter Control Register B – TCCR2B

• Bit 7 – FOC2A: Force Output Compare A

The FOC2A bit is only active when the WGM bits specify a non-PWM mode.

However, for ensuring compatibility with future devices, this bit must be set to zero when

TCCR2B is written when operating in PWM mode. When writing a logical one to the FOC2A bit,

an immediate Compare Match is forced on the Waveform Generation unit. The OC2A output is

changed according to its COM2A1:0 bits setting. Note that the FOC2A bit is implemented as a

strobe. Therefore it is the value present in the COM2A1:0 bits that determines the effect of the

forced compare.

A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using

OCR2A as TOP.

The FOC2A bit is always read as zero.

• Bit 6 – FOC2B: Force Output Compare B

The FOC2B bit is only active when the WGM bits specify a non-PWM mode.

However, for ensuring compatibility with future devices, this bit must be set to zero when

TCCR2B is written when operating in PWM mode. When writing a logical one to the FOC2B bit,

an immediate Compare Match is forced on the Waveform Generation unit. The OC2B output is

changed according to its COM2B1:0 bits setting. Note that the FOC2B bit is implemented as a

strobe. Therefore it is the value present in the COM2B1:0 bits that determines the effect of the

forced compare.

A FOC2B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using

OCR2B as TOP.

The FOC2B bit is always read as zero.

• Bits 5:4 – Res: Reserved Bits

These bits are reserved bits in the ATmega48/88/168 and will always read as zero.

• Bit 3 – WGM22: Waveform Generation Mode

See the description in the “Timer/Counter Control Register A – TCCR2A” on page 146.

• Bit 2:0 – CS22:0: Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table

15-8.

Bit

210

FOC2A

FOC2B

–

WGM22

CS22

CS21

CS20

TCCR2B

Read/Write

R/W

Initial Value

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