STMicroelectronics STM32F05 series Reference Manual page 547

RM0091
Timestamp on tamper event:
With TAMPTS set to '1', any tamper event causes a timestamp to occur. In this case, either
the TSF bit or the TSOVF bit are set in RTC_ISR, in the same manner as if a normal
timestamp event occurs. The affected tamper flag register TAMPxF is set at the same time
that TSF or TSOVF is set.
Edge detection on tamper inputs
If the TAMPFLT bits are "00", the RTC_TAMPx pins generate tamper detection events when
either a rising edge or a falling edge is observed depending on the corresponding
TAMPxTRG bit. The internal pull-up resistors on the RTC_TAMPx inputs are deactivated
when edge detection is selected.
Caution: To avoid losing tamper detection events, the signal used for edge detection is logically
ANDed with the corresponding TAMPxE bit in order to detect a tamper detection event in
case it occurs before the RTC_TAMPx pin is enabled.
● When TAMPxTRG = 0: if the RTC_TAMPx alternate function is already high before
tamper detection is enabled (TAMPxE bit set to 1), a tamper event is detected as soon
as the RTC_TAMPx input is enabled, even if there was no rising edge on the
RTC_TAMPx input after TAMPxE was set.
●
When TAMPxTRG = 1: if the RTC_TAMPx alternate function is already low before
tamper detection is enabled, a tamper event is detected as soon as the RTC_TAMPx
input is enabled (even if there was no falling edge on the RTC_TAMPx input after
TAMPxE was set.
After a tamper event has been detected and cleared, the RTC_TAMPx alternate function
should be disabled and then re-enabled (TAMPxE set to 1) before re-programming the
backup registers (RTC_BKPxR). This prevents the application from writing to the backup
registers while the RTC_TAMPx input value still indicates a tamper detection. This is
equivalent to a level detection on the RTC_TAMPx alternate function input.
Note: Tamper detection is still active when V
of the backup registers, the pin to which the RTC_TAMPx alternate function is mapped
should be externally tied to the correct level.
Level detection with filtering on RTC_TAMPx inputs
Level detection with filtering is performed by setting TAMPFLT to a non-zero value. A tamper
detection event is generated when either 2, 4, or 8 (depending on TAMPFLT) consecutive
samples are observed at the level designated by the TAMPxTRG bits.
The RTC_TAMPx inputs are pre-charged through the I/O internal pull-up resistance before
its state is sampled, unless disabled by setting TAMPPUDIS to 1,The duration of the
precharge is determined by the TAMPPRCH bits, allowing for larger capacitances on the
RTC_TAMPx inputs.
The trade-off between tamper detection latency and power consumption through the pull-up
can be optimized by using TAMPFREQ to determine the frequency of the sampling for level
detection.
Note: Refer to the datasheets for the electrical characteristics of the pull-up resistors.
power is switched off. To avoid unwanted resetting
DD
Doc ID 018940 Rev 1
Real-time clock (RTC)
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