Rcc Clock Configuration Register (Rcc_Cfgr) - ST STM32F423 Reference Manual

RM0430
Bits 5:0 PLLM[5:0]: Division factor for the main PLL (PLL) input clock
Caution: The software has to set these bits correctly to ensure that the VCO input frequency
6.3.3

RCC clock configuration register (RCC_CFGR)

Address offset: 0x08
Reset value: 0x0000 0000
Access: 0
1 or 2 wait states inserted only if the access occurs during a clock source switch.
31 30 29
MCO2[1:0] MCO2 PRE[2:0]
rw rw rw
15 14 13
PPRE2[2:0]
rw rw rw
Bits 31:30 MCO2[1:0]: Microcontroller clock output 2
Set and cleared by software. Clock source selection may generate glitches on MCO2. It is
highly recommended to configure these bits only after reset before enabling the external
oscillators and the PLLs.
00: System clock (SYSCLK) selected
01: PLLI2S clock selected
10: HSE oscillator clock selected
11: PLL clock selected
Set and cleared by software to divide the PLL and PLLI2S input clock before the VCO.
These bits can be written only when the PLL and PLLI2S are disabled.
ranges from 1 to 2 MHz. It is recommended to select a frequency of 2 MHz to limit
PLL jitter.
VCO input frequency = PLL input clock frequency / PLLM with 2 ≤ PLLM ≤ 63
000000: PLLM = 0, wrong configuration
000001: PLLM = 1, wrong configuration
000010: PLLM = 2
000011: PLLM = 3
000100: PLLM = 4
...
111110: PLLM = 62
111111: PLLM = 63
wait state 2, word, half-word and byte access
≤ ≤
28 27 26 25
MCO1 PRE[2:0]
rw rw rw rw
12 11 10 9
PPRE1[2:0] Res.
rw rw rw
Reset and clock control (RCC) for STM32F413/423
24 23 22
Res. MCO1[1:0]
rw rw
8 7 6
Res. HPRE[3:0]
rw rw
RM0430 Rev 8
21 20 19 18
RTCPRE[4:0]
rw rw rw
5 4 3 2
SWS[1:0]
rw rw r r
17 16
rw rw
1 0
SW[1:0]
rw rw
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