AN3371 datasheet(25/45 Pages) STMICROELECTRONICS

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AN3371

Overview of the STM32 advanced RTC

Doc ID 018624 Rev 5

25/45

1.8.3

Active time-stamp on tamper detection event

By setting the TAMPTS bit to 1, any tamper event (with edge or level detection) causes a

time-stamp to occur. Consequently, the time-stamp flag and time-stamp overflow flag are set

at the moment when the tamper flag is set and work in the same manner as when a normal

time-stamp event occurs.

Note:

It is not necessary to enable or disable the time-stamp function when using this feature.

1.9

Backup registers

RTC_BKPxR, where x=0 to n backup registers (80 bytes), are reset when a tamper

detection event occurs. These registers are powered-on by VBAT when VDD is switched off,

so that they are not reset by a system reset, and their contents remain valid when the device

operates in low-power mode.

Note:

The number “n” of backup registers depends on the product. Please refer to Table 15:

Advanced RTC features.

1.10

RTC and low-power modes

The RTC is designed to minimize the power consumption. The prescalers used for the

calendar are divided into synchronous and asynchronous.

Increasing the value of the asynchronous prescaler reduces the power consumption.

Table 13.

Tamper features (level detection)

What to do

How to do it

Comments

Enable Tamper

Set the TAMP1E bit of

RTC_TAFCR register to 1

Configure Tamper1 filter

count

Configure TAMPFLt bits in

RTC_TAFCR register

Default value is 0.

Configure Tamper1 sampling

frequency

Configure TAMPFREQ bits

in RTC_TAFCR register

Default value is 1Hz

Configure tamper

precharge/discharge

duration

Set/Reset TAMPPUDIS bit

in RTC_TAMPCR register

select Tamper1 active

edge/Level detection

Select with TAMP1TRG bit

in RTC_TAFCR register

Edge or Level is depending on tamper

filter configuration.

Map Tamper1 pin alternate

function

Select with TAMP1INSEL

bit in RTC_TAFCR register

For F2 series devices, the Tamper1 pin

can be either PI8 or PC13.

Detect a Tamper1event by

interrupt

Set the TAMPIE bit in the

RTC_TAFCR register

An interrupt is generated when

tamper detection event occurs.

Detect a Tamper1 event by

polling

Poll on the time-stamp

flag (TAMP1F) in the

RTC_ISR register

To clear the flag, write zero on the

TAMP1F bit.

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