21.3.3.1 Normal Operation

In ordinary operation, the counter counts clock ticks in the direction selected by the Direction (DIR) bit in the Control E (TCAn.CTRLE) register until it reaches TOP or BOTTOM. The peripheral clock (CLK_PER), prescaled according to the Clock Select (CLKSEL) bit field in the Control A (TCAn.CTRLA) register, gives the clock ticks.

When TOP is reached while the counter is counting up, the counter will wrap to ‘0’ at the next clock tick. When counting down, the counter is reloaded with the Period (TCAn.PER) register value when the BOTTOM is reached.

It is possible to change the counter value in the Counter (TCAn.CNT) register when the counter is running. The write access to TCAn.CNT register has higher priority than count, clear or reload, and will be immediate. The direction of the counter can also be changed during ordinary operation by writing to the Direction (DIR) bit in the Control E (TCAn.CTRLE) register.