ATtiny5 datasheet(57/168 Pages) ATMEL

57 / 168 page

8127C–AVR–10/09

ATtiny4/5/9/10

11.5 Input Capture Unit

The Timer/Counter incorporates an Input Capture unit that can capture external events and give

them a time-stamp indicating time of occurrence. The external signal indicating an event, or mul-

tiple events, can be applied via the ICP0 pin. The time-stamps can then be used to calculate

frequency, duty-cycle, and other features of the signal applied. Alternatively the time-stamps can

be used for creating a log of the events.

The Input Capture unit is illustrated by the block diagram shown in Figure 11-5 on page 57. The

elements of the block diagram that are not directly a part of the Input Capture unit are gray

shaded. The lower case “n” in register and bit names indicates the Timer/Counter number.

Figure 11-5. Input Capture Unit Block Diagram

When a change of the logic level (an event) occurs on the Input Capture pin (ICP0), alternatively

on the Analog Comparator output (ACO), and this change confirms to the setting of the edge

detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter

(TCNT0) is written to the Input Capture Register (ICR0). The Input Capture Flag (ICF0) is set at

the same system clock as the TCNT0 value is copied into ICR0 Register. If enabled (ICIE0 = 1),

the Input Capture Flag generates an Input Capture interrupt. The ICF0 flag is automatically

cleared when the interrupt is executed. Alternatively the ICF0 flag can be cleared by software by

writing a logical one to its I/O bit location.

Reading the 16-bit value in the Input Capture Register (ICR0) is done by first reading the low

byte (ICR0L) and then the high byte (ICR0H). When the low byte is read the high byte is copied

into the high byte temporary register (TEMP). When the CPU reads the ICR0H I/O location it will

access the TEMP Register.

The ICR0 Register can only be written when using a Waveform Generation mode that utilizes

the ICR0 Register for defining the counter’s TOP value. In these cases the Waveform Genera-

ICFn (Int.Req.)

Analog

Comparator

WRITE

ICRn (16-bit Register)

ICRnH (8-bit)

Noise

Canceler

ICPn

Edge

Detector

TEMP (8-bit)

DATA BUS (8-bit)

ICRnL (8-bit)

TCNTn (16-bit Counter)

TCNTnH (8-bit)

TCNTnL (8-bit)

ACIC*

ICNC

ICES

ACO*

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