STM32F207IE datasheet(23/163 Pages) STMICROELECTRONICS

23 / 163 page

STM32F205xx, STM32F207xx

Description

Doc ID 15818 Rev 7

23/163

Figure 7.

Startup in regulator OFF: fast VDD slope

- power-down reset risen before VCAP_1/VCAP_2 stabilization

2.2.18

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

The backup domain of the STM32F205xx and STM32F207xx 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. Dedicated registers contain

the second, minute, hour (in 12/24 hour), week day, date, month, year, in BCD (binary-coded

decimal) format. Correction for 28, 29 (leap year), 30, and 31 day of the month are

performed automatically. The RTC provides a 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.

The backup SRAM size is 4 Kbytes and can be enabled by software. When the backup RAM

is enabled the power consumption in Standby or VBAT mode is slightly higher (see

Section 2.2.19: Low-power modes).

The backup registers are 32-bit registers used to store 80 bytes of user application data

when VDD power is not present. Backup registers are not reset by a system, a power reset,

or when the device wakes up from the Standby mode (see Section 2.2.19: Low-power

modes).

The RTC, backup RAM and backup registers are supplied through a switch that takes power

from either the VDD supply when present or the VBAT pin.

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