Datasheet

7734Q–AVR–02/12

AT90PWM81/161

11.8 16-bit Timer/Counter Register Description

11.8.1 TCCR1B - Timer/Counter1 Control Register B

• 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 3 – Reserved

• Bit 2:0 – CS12:0: Clock Select

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

Table 11-2.

Bit 76543 210

ICNC1 ICES1 - WGM13 - CS12 CS11 CS10 TCCR1B

Read/Write R/W R/W R R/W R R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 4 – WGM13: Waveform Generation Mode

See Table 11-1 for the modes definition

Table 11-1. Waveform generation mode bit description.

Mode WGM13

Timer/counter mode of

operation TOP

TOV1 flag

set on

0 0 Normal 0xFFFF MAX

12 1 CTC ICR1 MAX

Table 11-2. Clock select bit description.

CS12 CS11 CS10 Description

0 0 0 No clock source (Timer/Counter stopped)

001clkI/O/1 (No prescaling)

010Reserved