Events

The TCA can generate the events described in the table below. All event generators except TCAn_HUNF are shared between Normal mode and Split mode operation, and the generator name indicates what specific signal the generator represents in each mode in the following way: OVF_LUNF corresponds to overflow in Normal mode and Low byte timer underflow in Split mode. The same applies to CMPn_LCMPn.

Table 1. Event Generators in TCA
Generator Name		Description	Event Type	Generating Clock Domain	Length of Event
Peripheral	Event	Description	Event Type	Generating Clock Domain	Length of Event
TCAn	OVF_LUNF	Normal mode: Overflow Split mode: Low byte timer underflow	Pulse	CLK_PER	One CLK_PER period
	HUNF	Normal mode: Not available Split mode: High byte timer underflow	Pulse	CLK_PER	One CLK_PER period
	CMP0_LCMP0	Normal mode: Compare Channel 0 match Split mode: Low byte timer Compare Channel 0 match	Pulse	CLK_PER	One CLK_PER period
	CMP1_LCMP1	Normal mode: Compare Channel 1 match Split mode: Low byte timer Compare Channel 1 match	Pulse	CLK_PER	One CLK_PER period
	CMP2_LCMP2	Normal mode: Compare Channel 2 match Split mode: Low byte timer Compare Channel 2 match	Pulse	CLK_PER	One CLK_PER period

Note: The conditions for generating an event are identical to those that will raise the corresponding interrupt flag in the TCAn.INTFLAGS register for both Normal mode and Split mode.

The TCA has two event users for detecting and acting upon input events. The table below describes the event users and their associated functionality.

Table 2. Event Users in TCA
User Name		Description	Input Detection	Async/Sync
Peripheral	Input	Description	Input Detection	Async/Sync
TCAn	CNTA	Count on a positive event edge	Edge	Sync
		Count on any event edge	Edge	Sync
		Count while the event signal is high	Level	Sync
		The event level controls the count direction, up when low and down when high	Level	Sync
	CNTB	The event level controls count direction, up when low and down when high	Level	Sync
		Restart counter on a positive event edge	Edge	Sync
		Restart counter on any event edge	Edge	Sync
		Restart counter while the event signal is high	Level	Sync

The specific actions described in the table above are selected by writing to the Event Action (EVACTA, EVACTB) bits in the Event Control (TCAn.EVCTRL) register. Input events are enabled by writing a ‘1’ to the Enable Counter Event Input (CNTAEI and CNTBEI) bits in the TCAn.EVCTRL register.

If both EVACTA and EVACTB are configured to control the count direction, the event signals will be OR’ed to determine the count direction. Both event inputs must then be low for the counter to count upwards.

Notes:

1.Event inputs are not used in Split mode.
2.Event actions with level input detection only work reliably if the event frequency is less than the timer’s frequency.

Refer to the Event System (EVSYS) section for more details regarding event types and Event System configuration.

ATtiny1624/1626/1627

Events