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157

XMEGA A [MANUAL]

8077I–AVR–11/2012

Figure 14-9. Changing the period using buffering.

14.7

Capture Channel

The CC channels can be used as capture channels to capture external events and give them a timestamp. To use

capture, the counter must be set for normal operation.

Events are used to trigger the capture; i.e., any events from the event system, including pin change from any pin, can

trigger a capture operation. The event source select setting selects which event channel will trigger CC channel A. The

subsequent event channels then trigger events on subsequent CC channels, if configured. For example, setting the

event source select to event channel 2 results in CC channel A being triggered by event channel 2, CC channel B

triggered by event channel 3, and so on.

Figure 14-10.Event source selection for capture operation.

The event action setting in the timer/counter will determine the type of capture that is done.

The CC channels must be enabled individually before capture can be done. When the capture condition occur, the

timer/counter will time-stamp the event by copying the current CNT value in the count register into the enabled CC

channel register.

When an I/O pin is used as an event source for the capture, the pin must be configured for edge sensing. For details on

sense configuration on I/O pins, refer to “Input Sense Configuration” on page 136. If the period register value is lower

than 0x8000, the polarity of the I/O pin edge will be stored in the most-significant bit (msb) of the capture register. If the

msb of the capture register is zero, a falling edge generated the capture. If the msb is one, a rising edge generated the

capture.

14.7.1 Input Capture

Selecting the input capture event action makes the enabled capture channel perform an input capture on an event. The

interrupt flags will be set and indicate that there is a valid capture result in the corresponding CC register. At the same

time, the buffer valid flags indicate valid data in the buffer registers.

The counter will continuously count from BOTTOM to TOP, and then restart at BOTTOM, as shown in Figure 14-11. The

figure also shows four capture events for one capture channel.

CNT

MAX

New Period written to

PERBUF that is higher

than current CNT

New Period written to

PERBUF that is lower

than current CNT

"update"

"write"

New PER is updated

with PERBUF value.

BOTTOM

Event System

CH0MUX

CH1MUX

CHnMUX

Rotate

Event channel n

Event Source Selection

CCA capture

CCB capture

CCC capture

CCD capture

Event channel 0

Event channel 1

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