24.3.3.1.4 Input Capture Frequency Measurement Mode
In the Input Capture Frequency Measurement mode, the TCB captures the counter value and restarts on either a positive or negative edge of the event input signal.
The CAPT Interrupt flag is automatically cleared after the low byte of the Compare/Capture (TCBn.CCMP) register has been read. An OVF interrupt and event is generated when the CNT value is MAX.
This mode requires TCB to be configured as an event user and is explained in the Events section.
The figure below illustrates this mode when configured to act on a rising edge.