Datasheet

156
XMEGA B [DATASHEET]
8291B–AVR–01/2013
Figure 13-6. Normal operation.
As shown in Figure 13-6, it is possible to change the counter value when the counter is running. The write access has
higher priority than count, clear, or reload, and will be immediate. The direction of the counter can also be changed
during normal operation.
Normal operation must be used when using the counter as timer base for the capture channels.
13.6.2 Event Action Controlled Operation
The event selection and event action settings can be used to control the counter from the event system. For the counter,
the following event actions can be selected:
 Event system controlled up/down counting.
 Event n will be used as count enable.
 Event n+1 will be used to select between up (1) and down (0). The pin configuration must be set to low level
sensing.
 Event system controlled quadrature decode counting.
13.6.3 32-bit Operation
Two timer/counters can be used together to enable 32-bit counter operation. By using two timer/counters, the overflow
event from one timer/counter (least-significant timer) can be routed via the event system and used as the clock input for
another timer/counter (most-significant timer).
13.6.4 Changing the Period
The counter period is changed by writing a new TOP value to the period register. If double buffering is not used, any
period update is immediate, as shown in Figure 13-7 on page 156.
Figure 13-7. Changing the period without buffering.
CNT
BOTTOM
MAX
"update"
TOP
CNT written
DIR
CNT
MAX
New TOP written to
PER that is higher
than current CNT
Counter Wraparound
New TOP written to
PER that is lower
than current CNT
"update"
"write"
BOTTOM