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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