
Reset and clock control (RCC)
RM0453
278/1454
RM0453 Rev 2
7.1.3 Backup
domain
reset
The Backup domain has two specific resets.
A Backup domain reset is generated when one of the following events occurs:
•
a software reset, triggered by setting the BDRST bit in the
•
V
DD
or V
BAT
power on, if both supplies have previously been powered off
A Backup domain reset only affects the LSE oscillator, the RTC, the Backup registers and
the RCC Backup domain control register.
7.1.4 Sub-GHz
radio
reset
The sub-GHz radio can be reset by the RFRST register bit. A sub-GHz radio reset status
flag is provided in the RFRSTF register bit. The sub-GHz radio must not be accessed as
long as the reset status flag RFRSTF indicates sub-GHz radio in reset.
The sub-GHz radio is also reset when entering Shutdown mode.
7.1.5
PKA SRAM reset
The PKA SRAM is erased by hardware on any power reset and system reset. The status of
the PKA SRAM erase operation can be monitored in SYSCFG_SCSR.PKASRAMBSY flag
register bit.
7.2 Clocks
The following different clock sources can be used to drive the system clock (SYSCLK):
•
HSI16 (high-speed internal) 16 MHz RC oscillator clock
•
MSI (multi-speed internal) RC oscillator clock from 100 kHz to 48 MHz
•
HSE32 (high-speed external) 32 MHz oscillator clock, with trimming capacitors.
•
PLL clock
The MSI is used as system clock source after startup from reset, configured at 4 MHz.
The devices have the following additional clock sources:
•
LSI: 32 kHz low-speed internal RC that may drive the independent watchdog and
optionally the RTC used for auto-wakeup from Stop and Standby modes.
•
LSE: 32.768 kHz low-speed external crystal that optionally drives the RTC used for
auto-wakeup from Stop, Standby and Shutdown modes, or the real-time clock
(RTCCLK).
Each clock source can be switched on or off independently when it is not used, to optimize
power consumption.
Several prescalers can be used to configure the AHB frequencies (HCLK3/PCLK3, HCLK1,
HCLK2), the high-speed APB2 (PCLK2) and the low-speed APB1 (PCLK1) domains. The
maximum frequency of the AHB (HCLK3, HCLK1, and HCLK2), the PCLK1 and the PCLK2
domains is 48 MHz.