SAM4C_14 Datasheet, PDF (405/1303 Pages) ATMEL Corporation – Atmel | SMART ARM-based Flash MCU

20.4.9.2 Wake-up Inputs
The wake-up inputs WKUPx can be programmed to perform a system wake-up. Each input can be enabled by
setting the corresponding bit, WKUPENx, in the Wake-up Inputs register (SUPC_WUIR). The wake-up level can
be selected with the corresponding polarity bit, WKUPTx, also located in SUPC_WUIR.
A logical OR combination of all the resulting signals triggers a debouncing counterThe WKUPDBC field can be
configured to select a debouncing period of 3, 32, 512, 4,096 or 32,768 slow clock cycles. This corresponds,
respectively, to about 100 µs, about 1 ms, about 16 ms, about 128 ms and about 1 second (for a typical slow clock
frequency of 32 kHz). Configuring WKUPDBC to 0 selects an immediate wake-up, i.e., an enabled WKUP pin must
be active according to its polarity during a minimum of one slow clock period to wake up the core power supply.
If an enabled WKUPx pin holds the active polarity for a time longer than the debouncing period, a system wake-up
is started and the flags WKUPISx, as shown in Figure 20-4 and Figure 20-5, are reported in SUPC_SR. This
allows the user to identify the source of the wake-up. However, if a new wake-up condition occurs, the primary
information is lost. No new wake-up can be detected since the primary wake-up condition has disappeared.
20.4.9.3 Low-power Debouncer Inputs (Tamper Detection Pins)
Low-power debouncer inputs are dedicated to tamper detection. If the tamper sensor is biased through a resistor
and constantly driven by the power supply, this leads to power consumption as long as the tamper detection switch
is in its active state. To prevent power consumption when the switch is in active state, the tamper sensor circuitry
can be intermittently powered, thus, a specific waveform must be generated.
The waveform can be generated using pin RTCOUT0 in all modes, including Backup mode. Refer to the section
“Real-Time Counter (RTC)” section for waveform generation.
For SAM4C16/8 devices, separate debouncers are embedded, one for WKUP0/TMP0 input and a shared one for
WKUP10/TMP1, WKUP14/TMP2, WKUP15/TMP3 inputs. See Figure 20-4.
For SAM4C32 devices, separate debouncers are embedded for each wake-up/tamper input. See Figure 20-5.
The WKUP0/TMP0 and/or WKUP10/TMP1, WKUP14/TMP2, WKUP15/TMP3 inputs can be programmed to
perform a system wake-up with a debouncing done by RTCOUT0. This can be enabled by setting
LPDBCEN0/1/2/3 in SUPC_WUMR.
These inputs can be also used when VDDCORE is powered to obtain the tamper detection function with a low
power debounce function and to raise an interrupt.
The low-power debounce 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 20-6 shows an example of an application where two tamper switches are used. RTCOUT0 powers the
external pull-up used by the tampers.
SAM4C Series [DATASHEET]
Atmel-11102E-ATARM-SAM4C32-SAM4C16-SAM4C8-Datasheet_06-Oct-14
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