AN3371 datasheet(24/45 Pages) STMICROELECTRONICS

24 / 45 page

Overview of the STM32 advanced RTC

AN3371

24/45

Doc ID 018624 Rev 5

Figure 16. Tamper with level detection

Using the level detection (tamper filter set to a non-zero value), the tamper input pin can be

precharged by resetting TAMPUDIS through an internal resistance before sampling its state.

In order to support the different capacitance values, the length of the pulse during which the

internal pullup is applied can be 1, 2, 4 or 8 RTCCLK cycles.

Figure 17. Tamper sampling with precharge pulse

Note:

When the internal pullup is not applied, the I/Os Schmitt triggers are disabled in order to

avoid extra consumption if the tamper switch is open.

The trade-off between the tamper detection latency (using the precharge feature) and the

power consumption through the weak pullup/pulldown can be reduced by using a tamper

sampling frequency feature.

The tamper sampling frequency is determined by configuring the TAMPFREQ bits in the

RTC_TAMP register.

Note:

When using the LSE (32768 Hz) as the RTC clock source, the sampling frequency can be 1,

2, 4, 8, 16, 32, 64, or 128 Hz.

MS30114V1

RTC_TAMP1

RTC_TAMPx

STM32

Level detection

Tamper 1

switch

Tamper x

switch

MS30115V1

Start sampling

Precharge = 1RTCCLK

Precharge = 2RTCCLK

Precharge =4RTCCLK

RTC clock

Floating input

Switch opened

AN3371 Datasheet(PDF) 24 Page - STMicroelectronics