RM0453 Rev 5 307/1450
RM0453 Reset and clock control (RCC)
371
7.4 RCC registers
7.4.1 RCC clock control register (RCC_CR)
Address offset: 0x000
Reset value: 0x0000 0061
Access: no wait state, word, half-word and byte access
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. Res. Res. Res. Res. Res.
PLL
RDY
PLLON Res. Res.
HSEBY
PPWR
HSE
PRE
CSS
ON
Res.
HSE
RDY
HSEON
rrw rwrwrs rrw
1514131211109 8 765432 1 0
Res. Res. Res.
HSI
KERDY
HSI
ASFS
HSI
RDY
HSI
KERON
HSION MSIRANGE[3:0]
MSIRG
SEL
MSI
PLLEN
MSI
RDY
MSION
r rw r rw rw rw rw rw rw rs rw r rw
Bits 31:26 Reserved, must be kept at reset value.
Bit 25 PLLRDY: Main PLL clock ready flag
This bit is set by hardware to indicate that the main PLL is locked.
0: PLL unlocked
1: PLL locked
Bit 24 PLLON: Main PLL enable
This bit is set and cleared by software to enable the main PLL. It is also cleared by hardware
when entering Stop, Standby or Shutdown mode. This bit cannot be reset if the main PLL
clock is used as the system clock.
0: Main PLL off
1: Main PLL on
Bits 23:22 Reserved, must be kept at reset value.
Bit 21 HSEBYPPWR: HSE32 VDDTCXO output on package pin PB0-VDDTCXO enable
This bit is set and cleared by software to control the function on package pin
PB0-VDDTCXO. It can only be written when HSE32 oscillator is disabled
(HSEON = HSERDY = 0).
0: PB0 selected
1: VDDTCXO selected
Bit 20 HSEPRE: HSE32 SYSCLK prescaler
This bit is set and cleared by software to control the division factor of SYSCLK when
selecting HSE32 clock.
0: SYSCLK not divided (HSE32)
1: SYSCLK divided by two (HSE32 / 2)
Bit 19 CSSON: HSE32 clock security system enable
This bit is set by software to enable the clock security system. When CSSON is set, the
HSE32 lock detector is enabled by hardware when the HSE32 oscillator is ready, and
disabled by hardware if a HSE32 clock failure is detected. This bit is set only and is cleared
by reset.
0: HSE32 CSS off (clock detector off)
1: HSE32 CSS on (clock detector on if the HSE32 oscillator is stable and off if not)
Bit 18 Reserved, must be kept at reset value.
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