ATMEGA640 datasheet(185/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

20.10.2

TCCR2B – Timer/Counter Control Register B

• 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 and will always read as zero.

• Bit 3 – WGM22: Waveform Generation Mode

See the description in the “TCCR2A –Timer/Counter Control Register A” on page 182.

• 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 20-9.

Bit

210

(0xB1)

FOC2A

FOC2B

–

WGM22

CS22

CS21

CS20

TCCR2B

Read/Write

R/W

Initial Value

Table 20-9.

Clock Select Bit Description

CS22

CS21

CS20

Description

No clock source (Timer/Counter stopped)

clkT2S/(No prescaling)

clkT2S/8 (From prescaler)

clkT2S/32 (From prescaler)

clkT2S/64 (From prescaler)

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