PCIF0 datasheet(120/294 Pages) ATMEL

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120

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected

by the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt.

12.6

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 multiple events, can be applied via the ICP1 pin or alternatively, via the analog-comparator

unit. 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 12-3. The elements

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

Figure 12-3. Input Capture Unit Block Diagram

When a change of the logic level (an event) occurs on the Input Capture pin (ICP1), alterna-

tively 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 (TCNT1) is written to the Input Capture Register (ICR1). The Input Capture Flag

(ICF1) is set at the same system clock as the TCNT1 value is copied into ICR1 Register. If

enabled (ICIE1 = 1), the Input Capture Flag generates an Input Capture interrupt. The ICF1

flag is automatically cleared when the interrupt is executed. Alternatively the ICF1 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 (ICR1) is done by first reading the low

byte (ICR1L) and then the high byte (ICR1H). When the low byte is read the high byte is cop-

ied into the high byte temporary register (TEMP). When the CPU reads the ICR1H I/O location

it will access the TEMP Register.

The ICR1 Register can only be written when using a Waveform Generation mode that utilizes

the ICR1 Register for defining the counter’s TOP value. In these cases the Waveform Genera-

tion mode (WGM13:0) bits must be set before the TOP value can be written to the ICR1

WRITE

ICRn (16-bit Register)

ICRnH (8-bit)

TEMP (8-bit)

DATA BUS (8-bit)

ICRnL (8-bit)

TCNTn (16-bit Counter)

TCNTnH (8-bit)

TCNTnL (8-bit)

ICF1n (Int.Req.)

Noise

Canceler

Edge

Detector

ACIC

ICNCn

ICESn

ICPn

Analog

Comparator

ACO

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