AT90USB646 datasheet(140/456 Pages) ATMEL

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140

7593L–AVR–09/12

AT90USB64/128

• Bit 2:0 – CSn2:0: Clock Select

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

14-8 on page 107 and Figure 14-9 on page 108.

If external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock the

counter even if the pin is configured as an output. This feature allows software control of the

counting.

15.10.5

TCCR1C – Timer/Counter1 Control Register C

15.10.6

TCCR3C – Timer/Counter3 Control Register C

• Bit 7 – FOCnA: Force Output Compare for Channel A

• Bit 6 – FOCnB: Force Output Compare for Channel B

• Bit 5 – FOCnC: Force Output Compare for Channel C

The FOCnA/FOCnB/FOCnC bits are only active when the WGMn3:0 bits specifies a non-PWM

mode. When writing a logical one to the FOCnA/FOCnB/FOCnC bit, an immediate compare

match is forced on the waveform generation unit. The OCnA/OCnB/OCnC output is changed

according to its COMnx1:0 bits setting. Note that the FOCnA/FOCnB/FOCnC bits are imple-

mented as strobes. Therefore it is the value present in the COMnx1:0 bits that determine the

effect of the forced compare.

A FOCnA/FOCnB/FOCnC strobe will not generate any interrupt nor will it clear the timer in Clear

Timer on Compare Match (CTC) mode using OCRnA as TOP.

The FOCnA/FOCnB/FOCnB bits are always read as zero.

• Bit 4:0 – Reserved bits

These bits are reserved for future use. For ensuring compatibility with future devices, these bits

must be written to zero when TCCRnC is written.

Table 15-5.

Clock Select bit description.

CSn2

CSn1

CSn0

Description

No clock source. (Timer/Counter stopped)

clk

I/O/1 (no prescaling

clkI/O/8 (from prescaler)

clkI/O/64 (from prescaler)

clk

I/O/256 (from prescaler)

clkI/O/1024 (from prescaler)

External clock source on Tn pin. Clock on falling edge

External clock source on Tn pin. Clock on rising edge

Bit

210

FOC1A

FOC1B

FOC1C

–

TCCR1C

Read/write

RRR

Initial value

Bit

210

FOC3A

FOC3B

FOC3C

–

TCCR3C

Read/write

RRR

Initial value

AT90USB646 Datasheet(PDF) 140 Page - ATMEL Corporation

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