Datasheet

443
Atmel | SMART SAM D20 [DATASHEET]
Atmel-42129K–SAM-D20_datasheet–06/2014
When counting up a change from a top value that is lower relative to the old top value can make the counter miss this
change if the counter value is larger than the new top value when the change occurred. This will make the counter count
to the max value. An example of this can be seen in Figure 27-8.
Figure 27-8. Changing the Top Value when Counting Up
27.6.2.7 Capture Operations
To enable and use capture operations, the event line into the TC must be enabled using the TC Event Input bit in the
Event Control register (EVCTRL.TCEI). The capture channels to be used must also be enabled in the Capture Channel x
Enable bit group in the Control C register (CTRLC.CPTENx) before capture can be performed.
Event Capture Action
The compare/capture channels can be used as input capture channels to capture any event from the Event System and
give them a timestamp. Because all capture channels use the same event line, only one capture channel should be
enabled at a time when performing event capture.
Figure 27-9 shows four capture events for one capture channel.
Figure 27-9. Input Capture Timing
When the Capture Interrupt flag is set and a new capture event is detected, there is nowhere to store the new timestamp.
As a result, the Error Interrupt flag in the Interrupt Flag Status and Clear register (INTFLAG.ERR) is set.
COUNT
MAX
Counter Wraparound
"wraparound "
"write"
ZERO
New TOP value
That is Lower than
Current COUNT
New TOP value
That is higher than
Current COUNT
events
COUNT
TOP
ZERO
Capture 0 Capture 1 Capture 2 Capture 3