STCOM Datasheet, PDF (27/58 Pages) STMicroelectronics – Powerline communication and application system-on-chip

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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