Atmel SAM4L-EK Atmel ATSAM4L-EK ATSAM4L-EK Data Sheet

42023E–SAM–07/2013

Figure 30-12. WAVSEL = 3 With Trigger

An external event can be programmed to be detected on one of the clock sources (XC0, XC1,
XC2) or TIOB. The external event selected can then be used as a trigger.

The External Event Selection field in CMRn (CMRn.EEVT) selects the external trigger. The
External Event Edge Selection field in CMRn (CMRn.EEVTEDG) defines the trigger edge for
each of the possible external triggers (rising, falling or both). If CMRn.EEVTEDG is written to
zero, no external event is defined.

If TIOB is defined as an external event signal (CMRn.EEVT = 0), TIOB is no longer used as an
output and the compare register B is not used to generate waveforms and subsequently no
IRQs. In this case the TC channel can only generate a waveform on TIOA.

When an external event is defined, it can be used as a trigger by writing a one to the
CMRn.ENETRG bit.

As in Capture mode, the SYNC signal and the software trigger are also available as triggers. RC
Compare can also be used as a trigger depending on the CMRn.WAVSEL field. 

The output controller defines the output level changes on TIOA and TIOB following an event.
TIOB control is used only if TIOB is defined as output (not as an external event).

The following events control TIOA and TIOB:

• software trigger

• external event

• RC compare

RA compare controls TIOA and RB compare controls TIOB. Each of these events can be pro-
grammed to set, clear or toggle the output as defined in the following fields in CMRn:

• RC Compare Effect on TIOB (CMRn.BCPC)

Time

Counter Value

TIOB

TIOA

Counter decremented by compare match 

with RC

0xFFFF

Waveform Examples

RC

RB

RA

Counter decremented by trigger

Counter incremented by trigger