ST STM32F301 6 Series Reference Manual page 103

RM0366
Bit 17 HSERDY: HSE clock ready flag
Set by hardware to indicate that the HSE oscillator is stable. This bit needs 6 cycles of the HSE
oscillator clock to fall down after HSEON reset.
0: HSE oscillator not ready
1: HSE oscillator ready
Bit 16 HSEON: HSE clock enable
Set and cleared by software.
Cleared by hardware to stop the HSE oscillator when entering Stop or Standby mode. This bit
cannot be reset if the HSE oscillator is used directly or indirectly as the system clock.
0: HSE oscillator OFF
1: HSE oscillator ON
Bits 15:8 HSICAL[7:0]: HSI clock calibration
These bits are initialized automatically at startup.
Bits 7:3 HSITRIM[4:0]: HSI clock trimming
These bits provide an additional user-programmable trimming value that is added to the
HSICAL[7:0] bits. It can be programmed to adjust to variations in voltage and temperature that
influence the frequency of the HSI.
The default value is 16, which, when added to the HSICAL value, should trim the HSI to 8 MHz
± 1%. The trimming step (F
Bit 2 Reserved, must be kept at reset value.
Bit 1 HSIRDY: HSI clock ready flag
Set by hardware to indicate that HSI oscillator is stable. After the HSION bit is cleared,
HSIRDY goes low after 6 HSI oscillator clock cycles.
0: HSI oscillator not ready
1: HSI oscillator ready
Bit 0 HSION: HSI clock enable
Set and cleared by software.
Set by hardware to force the HSI oscillator ON when leaving Stop or Standby mode or in case
of failure of the HSE crystal oscillator used directly or indirectly as system clock. This bit
cannot be reset if the HSI is used directly or indirectly as system clock or is selected to become
the system clock.
0: HSI oscillator OFF
1: HSI oscillator ON
) is around 40 kHz between two consecutive HSICAL steps.
hsitrim
RM0366 Rev 5
Reset and clock control (RCC)
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