Datasheet

295
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
18.4.7.2 Low Power Debouncer Inputs
It is possible to generate a waveform (RTCOUT0 and RTCOUT1) in all modes (including backup mode). It can be useful
to control an external sensor and/or tampering function without waking up the processor. Please refer to the RTC section
for waveform generation.
Two separate debouncers are embedded for WKUP0 and WKUP1 inputs.
The WKUP0 and/or WKUP1 inputs can be programmed to perform a wake up of the core power supply with a
debouncing done by RTCOUT0.
These inputs can be also used when VDDCORE is powered to get tamper detection function with a low power debounce
function.
This can be enabled by setting LPDBC0 bit and/or LPDBC1 bit in SUPC_WUMR.
In this mode of operation, WKUP0 and/or WKUP1 must not be configured to also act as debouncing source for the
WKUPDBC counter (WKUPEN0 and/or WKUPEN1 must be cleared in SUPC_WUIR). Refer to Figure 18-4.
This mode of operation requires the RTC Output (RTCOUT0) to be configured to generate a duty cycle programmable
pulse (i.e. OUT0 = 0x7 in RTC_MR) in order to create the sampling points of both debouncers. The sampling point is the
falling edge of the RTCOUT0 waveform.
Figure 18-5 shows an example of an application where two tamper switches are used. RTCOUT0 powers the external
pull-up used by the tampers.
Figure 18-5. Low Power Debouncer (Push-to-Make switch, pull-up resistors)
AT91SAM
WKUP0
WKUP1
RTCO U T0
Pull-Up
Resist or
Pull-Up
Resist or
GND
GND
GND