ATmega128 datasheet(136/386 Pages) ATMEL

136 / 386 page

136

2467S–AVR–07/09

ATmega128

Timer/Counter1

Control Register B –

TCCR1B

Timer/Counter3

Control Register B –

TCCR3B

• Bit 7 – ICNCn: Input Capture Noise Canceler

Setting this bit (to one) activates the Input Capture Noise Canceler. When the Noise Canceler is

activated, the input from the Input Capture Pin (ICPn) is filtered. The filter function requires four

successive equal valued samples of the ICPn pin for changing its output. The Input Capture is

therefore delayed by four Oscillator cycles when the noise canceler is enabled.

• Bit 6 – ICESn: Input Capture Edge Select

This bit selects which edge on the Input Capture Pin (ICPn) that is used to trigger a capture

event. When the ICESn bit is written to zero, a falling (negative) edge is used as trigger, and

when the ICESn bit is written to one, a rising (positive) edge will trigger the capture.

When a capture is triggered according to the ICESn setting, the counter value is copied into the

Input Capture Register (ICRn). The event will also set the Input Capture Flag (ICFn), and this

can be used to cause an Input Capture Interrupt, if this interrupt is enabled.

When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the

TCCRnA and the TCCRnB Register), the ICPn is disconnected and consequently the Input Cap-

ture function is disabled.

• Bit 5 – Reserved Bit

This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be

written to zero when TCCRnB is written.

• Bit 4:3 – WGMn3:2: Waveform Generation Mode

See TCCRnA Register description.

• 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

55 and Figure 56.

Bit

765

ICNC1

ICES1

–

WGM13

WGM12

CS12

CS11

CS10

TCCR1B

Read/Write

R/W

Initial Value

Bit

765

210

ICNC3

ICES3

–

WGM33

WGM32

CS32

CS31

CS30

TCCR3B

Read/Write

R/W

Initial Value

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