ATmega32A datasheet(115/352 Pages) ATMEL

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115

8155B–AVR–07/09

ATmega32A

• Bit 7 – ICNC1: 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 (ICP1) is filtered. The filter function requires four

successive equal valued samples of the ICP1 pin for changing its output. The Input Capture is

therefore delayed by four Oscillator cycles when the Noise Canceler is enabled.

• Bit 6 – ICES1: Input Capture Edge Select

This bit selects which edge on the Input Capture Pin (ICP1) that is used to trigger a capture

event. When the ICES1 bit is written to zero, a falling (negative) edge is used as trigger, and

when the ICES1 bit is written to one, a rising (positive) edge will trigger the capture.

When a capture is triggered according to the ICES1 setting, the counter value is copied into the

Input Capture Register (ICR1). The event will also set the Input Capture Flag (ICF1), and this

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

When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in the

TCCR1A and the TCCR1B Register), the ICP1 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 TCCR1B is written.

• Bit 4:3 – WGM13:2: Waveform Generation Mode

See TCCR1A Register description.

• Bit 2:0 – CS12:0: Clock Select

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

16-10 and Figure 16-11.

If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the

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

counting.

Table 16-6.

Clock Select Bit Description

CS12

CS11

CS10

Description

No clock source (Timer/Counter stopped).

001

clk

I/O/1 (No prescaling)

010

clkI/O/8 (From prescaler)

011

clk

I/O/64 (From prescaler)

100

clk

I/O/256 (From prescaler)

101

clkI/O/1024 (From prescaler)

External clock source on T1 pin. Clock on falling edge.

External clock source on T1 pin. Clock on rising edge.

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