Atmel SAM4L Xplained Pro Starter Kit Atmel ATSAM4L-XSTK ATSAM4L-XSTK Hoja De Datos

42023E–SAM–07/2013

The channel can also be configured to have an external trigger. In Capture mode, the external
trigger signal can be selected between TIOA and TIOB. In Waveform mode, an external event
can be programmed to be one of the following signals: TIOB, XC0, XC1, or XC2. This external
event can then be programmed to perform a trigger by writing a one to the External Event Trig-
ger Enable bit in CMRn (CMRn.ENETRG).

If an external trigger is used, the duration of the pulses must be longer than the CLK_TC period
in order to be detected.

Regardless of the trigger used, it will be taken into account at the following active edge of the
selected clock. This means that the counter value can be read differently from zero just after a
trigger, especially when a low frequency signal is selected as the clock.

The TIOA/TIOB input lines are ored internally with peripheral events from the Peripheral Event
System. To capture using events the user must ensure that the corresponding pin functions for
the TIOA/TIOB line are disabled. When capturing on the external TIOA/TIOB pin the user must
ensure that no peripheral events are generated on this pin.

This mode is entered by writing a zero to the CMRn.WAVE bit. 

Capture mode allows the TC channel to perform measurements such as pulse timing, fre-
quency, period, duty cycle and phase on TIOA and TIOB signals which are considered as
inputs. 

 shows the configuration of the TC channel when programmed in Cap-

ture mode.

Registers A and B (RA and RB) are used as capture registers. This means that they can be
loaded with the counter value when a programmable event occurs on the signal TIOA. 

The RA Loading Selection field in CMRn (CMRn.LDRA) defines the TIOA edge for the loading of
the RA register, and the RB Loading Selection field in CMRn (CMRn.LDRB) defines the TIOA
edge for the loading of the RB register.

RA is loaded only if it has not been loaded since the last trigger or if RB has been loaded since
the last loading of RA.

RB is loaded only if RA has been loaded since the last trigger or the last loading of RB.

Loading RA or RB before the read of the last value loaded sets the Load Overrun Status bit in
SRn (SRn.LOVRS). In this case, the old value is overwritten.

In addition to the SYNC signal, the software trigger and the RC compare trigger, an external trig-
ger can be defined.

The TIOA or TIOB External Trigger Selection bit in CMRn (CMRn.ABETRG) selects TIOA or
TIOB input signal as an external trigger. The External Trigger Edge Selection bit in CMRn
(CMRn.ETREDG) defines the edge (rising, falling or both) detected to generate an external trig-
ger. If CMRn.ETRGEDG is zero (none), the external trigger is disabled.