SAM3S_14 Datasheet, PDF (727/1087 Pages) ATMEL Corporation – AT91SAM ARM-based Flash MCU

If an external trigger is used, the duration of the pulses must be longer than the master clock period in order to be
detected.
35.6.7 Capture Operating Mode
This mode is entered by clearing the WAVE parameter in TC_CMR (Channel Mode Register).
Capture Mode allows the TC channel to perform measurements such as pulse timing, frequency, period, duty cycle
and phase on TIOA and TIOB signals which are considered as inputs.
Figure 35-5 shows the configuration of the TC channel when programmed in Capture Mode.
35.6.8 Capture Registers A and B
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 LDRA parameter in TC_CMR defines the TIOA selected edge for the loading of register A, and the LDRB
parameter defines the TIOA selected edge for the loading of Register B.
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 Overrun Error Flag (LOVRS) in TC_SR (Status
Register). In this case, the old value is overwritten.
35.6.9 Trigger Conditions
In addition to the SYNC signal, the software trigger and the RC compare trigger, an external trigger can be defined.
The ABETRG bit in TC_CMR selects TIOA or TIOB input signal as an external trigger. The ETRGEDG parameter
defines the edge (rising, falling or both) detected to generate an external trigger. If ETRGEDG = 0 (none), the
external trigger is disabled.
SAM3S [DATASHEET]
6500E–ATARM–11-Feb-13
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