Rainbow-electronics ATmega128RFA1 Manuel d'utilisateur télécharger pdf (Page 240)

240

8266A-MCU Wireless-12/09

ATmega128RFA1

17.9.3 TCCR0B – Timer/Counter0 Control Register B

Bit 7 6 5 4 3 2 1 0

$25 ($45) FOC0A FOC0B Res1 Res0 WGM02 CS02 CS01 CS00 TCCR0B

Read/Write W W R R RW RW RW RW

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – FOC0A - Force Output Compare A

The FOC0A bit is only active when the WGM02:0 bits specify a non-PWM mode.

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

when TCCR0B is written in a PWM operation mode. When writing a logical one to the

FOC0A bit, an immediate Compare Match is forced on the Waveform Generation unit.

The OC0A output is changed according to its COM0A1:0 bits setting. Note that the

FOC0A bit is implemented as a strobe. Therefore it is the value present in the

COM0A1:0 bits that determines the effect of the forced compare. A FOC0A strobe will

not generate any interrupt nor will it clear the timer in CTC mode using OCR0A as TOP.

The FOC0A bit is always read as zero.

• Bit 6 – FOC0B - Force Output Compare B

The FOC0B bit is only active when the WGM02:0 bits specify a non-PWM mode.

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

when TCCR0B is written in a PWM operation mode. When writing a logical one to the

FOC0B bit, an immediate Compare Match is forced on the Waveform Generation unit.

The OC0B output is changed according to its COM0B1:0 bits setting. Note that the

FOC0B bit is implemented as a strobe. Therefore it is the value present in the

COM0B1:0 bits that determines the effect of the forced compare. A FOC0B strobe will

not generate any interrupt nor will it clear the timer in CTC mode using OCR0B as TOP.

The FOC0B bit is always read as zero.

• Bit 5:4 – Res1:0 - Reserved Bit

This bit is reserved for future use. A read access always will return zero. A write access

does not modify the content.

• Bit 3 – WGM02 -

Combined with the WGM01:0 bit found in the TCCR0A Register, these bits control the

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

what type of waveform generation to be used. Modes of operation supported by the

Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare Match (CTC)

mode, and two types of Pulse Width Modulation (PWM) modes (see section "Modes of

Operation").

• Bit 2:0 – CS02:00 - Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter0

according to the following table.If external pin modes are used for Timer/Counter0,

transitions on the T0 pin will clock the counter even if the pin is configured as an output.

This feature allows software control of the counting.

Table 17-9 CS0 Register Bits

0x00 No clock source (Timer/Counter0 stopped)

0x01 clk_IO/1 (no prescaling)

0x02 clk_IO/8 (from prescaler)

CS02:00

0x03 clk_IO/64 (from prescaler)

1 2 ... 235 236 237 238 239 240 241 242 243 244 245 ... 523 524

Commentaires sur ces manuels

Pas de commentaire

Rainbow-electronics ATmega128RFA1 Manuel d'utilisateur Page 240

Commentaires sur ces manuels

Produits connexes et manuels pour Capteurs Rainbow-electronics ATmega128RFA1