ATMEGA640 datasheet(144/449 Pages) ATMEL

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ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

how waveforms are generated on the Output Compare outputs OCnx. For more details

about advanced counting sequences and waveform generation, see “Modes of Opera-

tion” on page 149.

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

selected by the WGMn3:0 bits. TOVn can be used for generating a CPU interrupt.

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 ICPn pin or alternatively, for the

Timer/Counter1 only, via the Analog Comparator unit. The time-stamps can then be

used to calculate frequency, duty-cycle, and other features of the signal applied. Alter-

natively 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 50. The ele-

ments of the block diagram that are not directly a part of the input capture unit are gray

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

Figure 50. Input Capture Unit Block Diagram

Note:

The Analog Comparator Output (ACO) can only trigger the Timer/Counter1 ICP – not

Timer/Counter3, 4 or 5.

When a change of the logic level (an event) occurs on the Input Capture Pin (ICPn),

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 (TCNTn) is written to the Input Capture Register (ICRn). The

Input Capture Flag (ICFn) is set at the same system clock as the TCNTn value is copied

into ICRn Register. If enabled (TICIEn = 1), the input capture flag generates an input

capture interrupt. The ICFn flag is automatically cleared when the interrupt is executed.

Alternatively the ICFn flag can be cleared by software by writing a logical one to its I/O

bit location.

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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