
RM0453 Rev 2
299/1454
RM0453
Reset and clock control (RCC)
363
Bit 8
HSION:
HSI16 clock enable
This bit is set and cleared by software. It is also cleared by hardware to stop the HSI16
oscillator when entering Stop, Standby or Shutdown mode. This bit is set by hardware to
force the HSI16 oscillator on when STOPWUCK = 1 or HSIASFS = 1 when exiting Stop
modes, or in case of HSE32 crystal oscillator failure.
This bit is set by hardware if the HSI16 is used directly or indirectly as system clock. This bit
cannot be reset if the HSI16 oscillator 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 = 1. The following frequency ranges 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 1 MHz
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)
Caution:
This field can be modified only when MSI is off (MSION = 0) or when MSI is ready
(MSIRDY = 1). This filed
must not
be modified when MSI is on and when MSI is
not
ready (MSION = 1 and MSIRDY = 0).
Bit 3
MSIRGSEL:
MSI range control selection
This bit is cleared to 0 on a system reset and when exiting Standby mode. It can be set to 1
by software. Software writing 0 has no effect.
0: MSI frequency range defined by MSISRANGE[3:0] in the RCC_CSR register
1: MSI frequency range defined by MSIRANGE[3:0] in the RCC_CR register
Bit 2
MSIPLLEN:
MSI clock PLL enable
This bit is set and cleared by software to enable/disable the PLL part of the MSI clock source.
It must be enabled after LSE is enabled (LSEON = 1) and ready (LSERDY set by
hardware).There is a hardware protection to avoid enabling this bit if LSE is not ready.
This bit is cleared by hardware when LSE is disabled (LSEON = 0) or when the CSS on LSE
detects an 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 and cleared by hardware to indicate that the MSI oscillator is stable or not. After
reset, this bit is read 1 once the MSI is ready.
0: MSI oscillator not ready
1: MSI oscillator ready
Note: Once MSION is cleared, MSIRDY goes low after six MSI clock cycles.