STMicroelectronics STM32WLEx Reference Manual page 238

Reset and clock control (RCC)
If the application is subject to voltage or temperature variations, this may affect the RC
oscillator speed. The HSI16 frequency can be trimmed in the application using the
HSITRIM[6:0] bits in the
For more details on how to measure the HSI16 frequency variation, refer to
Internal/external clock measurement with
The HSIRDY flag in the
stable or not. At startup, the HSI16 RC output clock is not released until this bit is set by
hardware.
The HSI16 RC can be switched on and off using the HSION bit in the
register (RCC_CR).
The HSI16 signal can also be used as a backup source (Auxiliary clock) if the HSE32 crystal
oscillator fails. Refer to
page 242.
6.2.3 MSI clock
The MSI clock signal is generated from an internal RC oscillator. Its frequency range can be
adjusted by software using the MSIRANGE[3:0] bits in the
(RCC_CR). The following frequency ranges are available: 100 kHz, 200 kHz, 400 kHz,
800 kHz, 1 MHz, 2 MHz, 4 MHz (default value), 8 MHz, 16 MHz, 24 MHz, 32 MHz and
48 MHz. To use the MSI range, it must be selected by MSIRGSEL.
The MSI clock is used as system clock after restart from Reset, wakeup from Standby and
Shutdown low-power modes. After restart from Reset and Shutdown, the MSI frequency is
set to its default value 4 MHz (see
Standby, MSI can be adjusted by software using the MSISRANGE[3:0] bits in the
control/status register
2 MHz, 4 MHz (default value) and 8 MHz.
The MSI clock can be selected as system clock after a wakeup from Stop mode (Stop 0,
Stop 1 or Stop 2, see
source (auxiliary clock for the CPU) if the HSE32 crystal oscillator fails (see
Clock security system on HSE32
The MSI RC oscillator provides a low-power clock source. In addition, when used in PLL-
mode with the LSE, it also provides a very accurate clock source that can be used to feed
the PLL to run the system at the maximum speed 48 MHz.
The MSIRDY flag in the
RC is stable or not. At startup, the MSI RC output clock is not released until this bit is set by
hardware. The MSI RC can be switched on and off by using the MSION bit in the
control register
Hardware auto calibration with LSE (PLL-mode)
When a 32.768 kHz external oscillator is present in the application, it is possible to configure
the MSI in a PLL-mode by setting the MSIPLLEN bit in the
(RCC_CR). When configured in PLL-mode, MSI automatically calibrates itself thanks to the
LSE. This mode is available for all MSI frequency ranges.
238/1306
RCC internal clock sources calibration register
RCC clock control register (RCC_CR)
Section 6.2.10: Clock security system on HSE32 (CSS) on
Section 6.3: Low-power
(RCC_CSR). The following frequency ranges are available: 1MHz,
Section 6.3: Low-power
(CSS)).
RCC clock control register (RCC_CR)
(RCC_CR).
RM0461 Rev 5
TIM16/TIM17.
indicates if the HSI16 RC is
RCC clock control register
modes). When wakeup from
modes). It can also be used as a backup clock
indicates whether the MSI
RCC clock control register
RM0461
(RCC_ICSCR).
Section 6.2.20:
RCC clock control
RCC
Section 6.2.10:
RCC clock