ST STM32F100 Series Reference Manual page 81

RM0041
Bit 16 HSEON: External high-speed clock enable
Set and cleared by software.
Cleared by hardware to stop the HSE oscillator when entering in 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]: Internal high-speed clock calibration
These bits are initialized automatically at startup.
Bits 7:3 HSITRIM[4:0]: Internal high-speed 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 internal HSI RC.
The default value is 16, which, when added to the HSICAL value, should trim the HSI to 8
MHz ± 1%. The trimming step (F
steps.
Bit 2 Reserved, always read as 0.
Bit 1 HSIRDY: Internal high-speed clock ready flag
Set by hardware to indicate that internal 8 MHz RC oscillator is stable. After the HSION bit is
cleared, HSIRDY goes low after 6 internal 8 MHz RC oscillator clock cycles.
0: internal 8 MHz RC oscillator not ready
1: internal 8 MHz RC oscillator ready
Bit 0 HSION: Internal high-speed clock enable
Set and cleared by software.
Set by hardware to force the internal 8 MHz RC oscillator ON when leaving Stop or Standby
mode or in case of failure of the HSE oscillator used directly or indirectly as system clock.
This bit cannot be reset if the internal 8 MHz RC is used directly or indirectly as system clock
or is selected to become the system clock.
0: internal 8 MHz RC oscillator OFF
1: internal 8 MHz RC oscillator ON
) is around 40 kHz between two consecutive HSICAL
hsitrim
RM0041 Rev 6
Reset and clock control (RCC)
81/709
101