Datasheet

324
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
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.
18.3.7.2 Low-power Tamper Detection and Anti-Tampering
Low-power debouncer inputs (WKUP0, WKUP1) can be used for 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 must be intermittently powered, and thus a specific waveform must be applied to the sensor circuitry.
The waveform is generated using RTCOUTx in all modes including backup mode. Refer to the RTC section for waveform
generation.
Separate debouncers are embedded, one for WKUP0 input, one for WKUP1 input.
The WKUP0 and/or WKUP1 inputs perform a system wake-up upon tamper detection. This is enabled by setting the
LPDBCEN0/1 bit in the ”Supply Controller Wake-up Mode Register” (SUPC_WUMR).
WKUP0 and/or WKUP1 inputs can also be used when VDDCORE is powered to detect a tamper.
When the bit LPDBCENx = 1, WKUPx pins must not be configured to act as a debouncing source for the WKUPDBC
counter (WKUPENx must be cleared in SUPC_WUIR).
Low-power tamper detection or debounce requires RTC output (RTCOUTx) 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 RTCOUTx waveform.
Figure 18-5 shows an example of an application where two tamper switches are used. RTCOUTx powers the external
pull-up used by the tamper sensor circuitry.
Figure 18-5. Low-power Debouncer (Push-to-Make Switch, Pull-up Resistors)
MCU
WKUP0
WKUP1
RTCOUTx
Pull-up
Resistor
Pull-up
Resistor
GND
GND
GND