STCOM05 datasheet(27/58 Pages) STMICROELECTRONICS

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STCOM

Description

VBAT operation

In case the RTC peripheral is used, the VBAT pin shall be supplied (2.0 V to 3.6 V) for the

RTC core operation and persistence of backup registers. An external battery or a similar

power source can be used.

The VBAT operation is activated, through an on-chip power switch, when the

DVDD_3V3_IO is not present. In this case the main core of the RTC and the backup

registers are under the VBAT domain.

The application can constantly monitor the health of the battery by reading the voltage level

present at the VBAT pin through the channel 7 of the general purpose 12-bit ADC.

A dedicated cutoff switch has been included to avoid continuous leakage from the battery

when the ADC is not sampling the line.

1.9

Low power modes

A clock gating is available for any peripheral in order to save all the dynamic power

contributes related the resources not used by the application.

The CPU is able to run at maximum frequency but, in case lower speed is sufficient to meet

the application requirements, also scaled values are allowed. The CPU could be in low

power modes waiting for wake-up events.

1.10

Real-time clock (RTC) and backup registers

The STCOM embeds an integrated real-time clock (RTC). The RTC provides a hardware

calendar implementation, instead of a simple 32-bit free-running counter. The calendar can

be initialized to set the current time/date of the system and provide information on sub-

seconds, seconds, minutes, hours (12 or 24 format), day (day of week), date (day of month),

month, and year.

Software can program the daylight saving compensation; it can control two programmable

alarms (with interrupt function) that can be triggered by any combination of the calendar

fields.

Synchronization can be done with an external clock using the sub-second shift feature.

RTC maskable interrupts/events are:



Alarms: two alarms are present



Timestamps: two timestamps are present



Tamper: two tamper detection inputs are present

The RTC is clocked with a 32.768 kHz external crystal and has coarse calibration (periodic

digital calibration), smooth calibration (0.954 ppm) and analog calibration functionalities.The

1 Hz /512 Hz internal reference clock is optionally available on RTC_TAMPB for calibration.

The RTC has also twenty 32-bit backup registers (80 bytes), available for user defined data

storage. The possibility that backup registers are reset when a tamper detection event

occurs is selectable by software.

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