STM32F207IE datasheet(28/178 Pages) STMICROELECTRONICS

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Functional overview

STM32F20xxx

28/178

DocID15818 Rev 11

3.16.3

Regulator ON/OFF and internal reset ON/OFF availability

3.17

Real-time clock (RTC), backup SRAM and backup registers

The backup domain of the STM32F20x devices includes:

•

The real-time clock (RTC)

•

4 Kbytes of backup SRAM

•

20 backup registers

The real-time clock (RTC) is an independent BCD timer/counter. Its main features are the

following:

•

Dedicated registers contain the second, minute, hour (in 12/24 hour), week day, date,

month, year, in BCD (binary-coded decimal) format.

•

Automatic correction for 28, 29 (leap year), 30, and 31 day of the month.

•

Programmable alarm and programmable periodic interrupts with wakeup from Stop and

Standby modes.

•

It is clocked by a 32.768 kHz external crystal, resonator or oscillator, the internal low-

power RC oscillator or the high-speed external clock divided by 128. The internal low-

speed RC has a typical frequency of 32 kHz. The RTC can be calibrated using an

external 512 Hz output to compensate for any natural quartz deviation.

•

Two alarm registers are used to generate an alarm at a specific time and calendar

fields can be independently masked for alarm comparison. To generate a periodic

interrupt, a 16-bit programmable binary auto-reload downcounter with programmable

resolution is available and allows automatic wakeup and periodic alarms from every

120 µs to every 36 hours.

•

A 20-bit prescaler is used for the time base clock. It is by default configured to generate

a time base of 1 second from a clock at 32.768 kHz.

•

Reference clock detection: a more precise second source clock (50 or 60 Hz) can be

used to enhance the calendar precision.

The 4-Kbyte backup SRAM is an EEPROM-like area.It can be used to store data which

need to be retained in VBAT and standby mode.This memory area is disabled to minimize

power consumption (see Section 3.18: Low-power modes). It can be enabled by software.

Table 4. Regulator ON/OFF and internal reset ON/OFF availability

Package

Regulator ON/internal

reset ON

Regulator

OFF/internal reset ON

Regulator OFF/internal

reset OFF

LQFP64

LQFP100

LQFP144

LQFP176

Yes

WLCSP 64+2

Yes

REGOFF and IRROFF

set to VSS

Yes

REGOFF set to VDD

and IRROFF set to VSS

Yes

REGOFF set to VSS and

IRROFF set to VDD

UFBGA176

Yes

REGOFF set to VSS

Yes

REGOFF set to VDD

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