Rainbow-electronics ATmega128RFA1 Uživatelský manuál stáhnout pdf (Strana 326)

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8266A-MCU Wireless-12/09

ATmega128RFA1

Table 21-9 WGM2 Register Bits

0x0 Normal mode of operation

0x1 PWM, phase correct, TOP=0xFF

0x2 CTC, TOP = OCRA

0x3 Fast PWM, TOP=0xFF

0x4 Reserved

0x5 PWM, Phase correct, TOP = OCRA

0x6 Reserved

WGM21:20

0x7 Fast PWM, TOP=OCRA

21.11.4 TCCR2B – Timer/Counter2 Control Register B

Bit 7 6 5 4 3 2 1 0

NA ($B1) FOC2A FOC2B Res1 Res0 WGM22 CS22 CS21 CS20 TCCR2B

Read/Write RW RW RW RW RW RW RW RW

Initial Value 0 0 0 0 0 0 0 0

• 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 in PWM mode operation. 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 in PWM mode operation. 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.

• Bit 5:4 – Res1:0 - Reserved

• Bit 3 – WGM22 - Waveform Generation Mode

Combined with the WGM21:0 bits found in the TCCR2A Register, this bit controls the

counting sequence of the counter, the source for maximum (TOP) counter value, and

what type of waveform generation to be used. See description of "TCCR2A -

Timer/Counter2 Control Register A" for details.

• Bit 2:0 – CS22:20 - Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter2. If

external pin modes are used for the Timer/Counter2, transitions on the T2 pin will clock

1 2 ... 321 322 323 324 325 326 327 328 329 330 331 ... 523 524

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