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XMEGA A [MANUAL]
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Figure 14-11.Input capture timing.
14.7.2 Frequency Capture
Selecting the frequency capture event action makes the enabled capture channel perform an input capture and restart on
positive edge events. This enables the timer/counter to measure the period or frequency of a signal directly. The capture
result will be the time (T) from the previous timer/counter restart until the event occurred. This can be used to calculate
the frequency (f) of the signal:
Figure 14-12.Frequency capture of an external signal.
Since all capture channels use the same counter (CNT), only one capture channel must be enabled at a time. If two
capture channels are used with different sources, the counter will be restarted on positive edge events from both input
sources, and the result will have no meaning.
14.7.3 Pulse Width Capture
Selecting the pulse width measure event action makes the enabled compare channel perform the input capture action on
falling edge events and the restart action on rising edge events. The counter will then restart on positive edge events,
and the input capture will be performed on the negative edge event. The event source must be an I/O pin, and the sense
events
CNT
TOP
BOTTOM
Capture 0
Capture 1
Capture 2
Capture 3
f
1
T
---
=
Period (T)
external signal
events
CNT
MAX
BOTTOM
"capture"