Reset and clock control (RCC) RM0033
86/1381 RM0033 Rev 9
5.1.3 Backup domain reset
The backup domain reset sets all RTC registers and the RCC_BDCR register to their reset
values. The BKPSRAM is not affected by this reset. The only way of resetting the
BKPSRAM is through the Flash interface by requesting a protection level change from 1 to
0.
A backup domain reset is generated when one of the following events occurs:
1. Software reset, triggered by setting the BDRST bit in the RCC Backup domain control
register (RCC_BDCR).
2. V
DD
or V
BAT
power on, if both supplies have previously been powered off.
5.2 Clocks
Three different clock sources can be used to drive the system clock (SYSCLK):
• HSI oscillator clock
• HSE oscillator clock
• Main PLL (PLL) clock
The devices have the two following secondary clock sources:
• 32 kHz low-speed internal RC (LSI RC) which drives the independent watchdog and,
optionally, the RTC used for Auto-wakeup from the Stop/Standby mode.
• 32.768 kHz low-speed external crystal (LSE crystal) which optionally drives the RTC
clock (RTCCLK)
Each clock source can be switched on or off independently when it is not used, to optimize
power consumption.
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