UM0306 Reset and clock control (RCC)
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Bit 18
HSEBYP External High Speed clock Bypass
Set and reset by software in debug for bypassing oscillator with external clock.
This bit can be written only if the external 1-25 MHz oscillator is disabled.
0: external 1-25 MHz oscillator not bypassed
1: external 1-25 MHz oscillator bypassed with external clock
Bit 17
HSERDY External High Speed clock ready flag
Set by hardware to indicate that external 1-25 MHz oscillator is stable. This bit
needs 6 cycles of external 1-25 MHz oscillator clock to fall down after HSEON
reset.
0: external 1-25 MHz oscillator not ready
1: external 1-25 MHz oscillator ready
Bit 16
HSEON External High Speed clock enable
Set and reset by software.
Reset by hardware to stop the external 1-25MHz oscillator when entering in
STOP and STANDBY mode. This bit can not be reset if the external 1-25 MHz
oscillator is used directly or indirectly as system clock or is selected to become
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 can be written by software to adjust calibration. They are added to the
value of the HSICAL[5:0] bits.
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. This bit
needs 6 cycles of the internal 8 MHz RC oscillator clock to fall down after HSION
reset.
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 reset by software.
Set by hardware to force the internal 8 MHz RC oscillator ON when leaving STOP
and STANDBY mode or in case of failure of the external 1-25 MHz oscillator used
directly or indirectly as system clock. This bit can not 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
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