The joint stream of prescaler ticks and event action ticks is called CLK_TCC_COUNT.
Figure 36-2. Prescaler
TCCx EV0/1
COUNT
PRESCALER
PRESCALER
EVACT 0/1
GCLK_TCC
GCLK_TCC /
{1,2,4,8,64,256,1024 }
CLK_TCC_COUNT
36.6.2.4. Counter Operation
Depending on the mode of operation, the counter is cleared, reloaded, incremented, or decremented at
each TCC clock input (CLK_TCC_COUNT). A counter clear or reload mark the end of current counter
cycle and the start of a new one.
The counting direction is set by the Direction bit in the Control B register (CTRLB.DIR). If the bit is zero,
it's counting up and one if counting down.
The counter will count up or down for each tick (clock or event) until it reaches TOP or ZERO. When it's
counting up and TOP is reached, the counter will be set to zero at the next tick (overflow) and the
Overflow Interrupt Flag in the Interrupt Flag Status and Clear register (INTFLAG.OVF) will be set. When
down-counting, the counter is reloaded with the TOP value when ZERO is reached (underflow), and
INTFLAG.OVF is set.
INTFLAG.OVF can be used to trigger an interrupt, or an event. An overflow/underflow occurrence (i.e. a
compare match with TOP/ZERO) will stop counting if the One-Shot bit in the Control B register is set
(CTRLBSET.ONESHOT).
Figure 36-3. Counter Operation
DIR
COUNT
MAX
"reload" update
TOP
COUNT written
Direction Change
Period (T)
ZERO
"clear" update
It is possible to change the counter value (by writing directly in the COUNT register) even when the
counter is running. The COUNT value will always be ZERO or TOP, depending on direction set by
CTRLBSET.DIR or CTRLBCLR.DIR, when starting the TCC, unless a different value has been written to
it, or the TCC has been stopped at a value other than ZERO. The write access has higher priority than
count, clear, or reload. The direction of the counter can also be changed during normal operation. See
also
Stop Command
A stop command can be issued from software by using TCC Command bits in Control B Set register
(CTRLBSET.CMD=0x2, STOP).
When a stop is detected while the counter is running, the counter will maintain its current value. If the
waveform generation (WG) is used, all waveforms are set to a state defined in Non-Recoverable State x
Atmel SAM L22G / L22J / L22N [DATASHEET]
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