DocID018909 Rev 11
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RM0090
Reset and clock control for STM32F42xxx and STM32F43xxx (RCC)
212
6.3.3 RCC
clock
configuration register (RCC_CFGR)
Address offset: 0x08
Reset value: 0x0000 0000
Access: 0
≤
wait state
≤
2, word, half-word and byte access
1 or 2 wait states inserted only if the access occurs during a clock source switch.
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
MCO2
MCO2 PRE[2:0]
MCO1 PRE[2:0]
I2SSC
R
MCO1
RTCPRE[4:0]
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
PPRE2[2:0]
PPRE1[2:0]
Reserved
HPRE[3:0]
SWS1
SWS0
SW1
SW0
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
r
r
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
Bits 27:29
MCO2PRE:
MCO2 prescaler
Set and cleared by software to configure the prescaler of the MCO2. Modification of this
prescaler may generate glitches on MCO2. It is highly recommended to change this
prescaler only after reset before enabling the external oscillators and the PLLs.
0xx: no division
100: division by 2
101: division by 3
110: division by 4
111: division by 5
Bits 24:26
MCO1PRE:
MCO1 prescaler
Set and cleared by software to configure the prescaler of the MCO1. Modification of this
prescaler may generate glitches on MCO1. It is highly recommended to change this
prescaler only after reset before enabling the external oscillators and the PLL.
0xx: no division
100: division by 2
101: division by 3
110: division by 4
111: division by 5
Bit 23
I2SSRC
:
I2S clock selection
Set and cleared by software. This bit allows to select the I2S clock source between the
PLLI2S clock and the external clock. It is highly recommended to change this bit only after
reset and before enabling the I2S module.
0: PLLI2S clock used as I2S clock source
1: External clock mapped on the I2S_CKIN pin used as I2S clock source