ST STM32L4x6 Reference Manual page 198

Reset and clock control (RCC)
Bit 8 HSION: HSI clock enable
Set and cleared by software.
Cleared by hardware to stop the HSI16 oscillator when entering Stop, Standby or Shutdown
mode.
Set by hardware to force the HSI16 oscillator ON when STOPWUCK=1 or HSIASFS = 1
when leaving Stop modes, or in case of failure of the HSE crystal oscillator.
This bit is set by hardware if the HSI16 is used directly or indirectly as system clock.
0: HSI16 oscillator OFF
1: HSI16 oscillator ON
Bits 7:4 MSIRANGE[3:0]: MSI clock ranges
These bits are configured by software to choose the frequency range of MSI when
MSIRGSEL is set.12 frequency ranges are available:
0000: range 0 around 100 kHz
0001: range 1 around 200 kHz
0010: range 2 around 400 kHz
0011: range 3 around 800 kHz
0100: range 4 around 1M Hz
0101: range 5 around 2 MHz
0110: range 6 around 4 MHz (reset value)
0111: range 7 around 8 MHz
1000: range 8 around 16 MHz
1001: range 9 around 24 MHz
1010: range 10 around 32 MHz
1011: range 11 around 48 MHz
others: not allowed (hardware write protection)
Note: Warning: MSIRANGE can be modified when MSI is OFF (MSION=0) or when MSI is
Bit 3 MSIRGSEL: MSI clock range selection
Set by software to select the MSI clock range with MSIRANGE[3:0]. Write 0 has no effect.
After a standby or a reset MSIRGSEL is at 0 and the MSI range value is provided by
MSISRANGE in CSR register.
0: MSI Range is provided by MSISRANGE[3:0] in RCC_CSR register
1: MSI Range is provided by MSIRANGE[3:0] in the RCC_CR register
Bit 2 MSIPLLEN: MSI clock PLL enable
Set and cleared by software to enable/ disable the PLL part of the MSI clock source.
MSIPLLEN must be enabled after LSE is enabled (LSEON enabled) and ready (LSERDY set
by hardware).There is a hardware protection to avoid enabling MSIPLLEN if LSE is not
ready.
This bit is cleared by hardware when LSE is disabled (LSEON = 0) or when the Clock
Security System on LSE detects a LSE failure (refer to RCC_CSR register).
0: MSI PLL OFF
1: MSI PLL ON
Bit 1 MSIRDY: MSI clock ready flag
This bit is set by hardware to indicate that the MSI oscillator is stable.
0: MSI oscillator not ready
1: MSI oscillator ready
Note: Once the MSION bit is cleared, MSIRDY goes low after 6 MSI clock cycles.
198/1693
ready (MSIRDY=1). MSIRANGE must NOT be modified when MSI is ON and NOT
ready (MSION=1 and MSIRDY=0)
DocID024597 Rev 3
RM0351