Reset and clock control for STM32F42xxx and STM32F43xxx (RCC)
RM0090
202/1731
DocID018909 Rev 11
6.3.22
RCC spread spectrum clock generation register (RCC_SSCGR)
Address offset: 0x80
Reset value: 0x0000 0000
Access: no wait state, word, half-word and byte access.
The spread spectrum clock generation is available only for the main PLL.
The RCC_SSCGR register must be written either before the main PLL is enabled or after
the main PLL disabled.
Note:
For full details about PLL spread spectrum clock generation (SSCG) characteristics, refer to
the “Electrical characteristics” section in your device datasheet.
Bits 23:2 Reserved, must be kept at reset value.
Bit 1
LSIRDY:
Internal low-speed oscillator ready
This bit is set and cleared by hardware to indicate when the internal RC 40 kHz oscillator is
stable. After the LSION bit is cleared, LSIRDY goes low after 3 LSI clock cycles.
0: LSI RC oscillator not ready
1: LSI RC oscillator ready
Bit 0
LSION:
Internal low-speed oscillator enable
This bit is set and cleared by software.
0: LSI RC oscillator OFF
1: LSI RC oscillator ON
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
SSCG
EN
SPR
EAD
SEL
Reserved
INCSTEP
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
INCSTEP
MODPER
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
Bit 31
SSCGEN:
Spread spectrum modulation enable
This bit is set and cleared by software.
0: Spread spectrum modulation DISABLE. (To write after clearing CR[24]=PLLON bit)
1: Spread spectrum modulation ENABLE. (To write before setting CR[24]=PLLON bit)
Bit 30
SPREADSEL:
Spread Select
This bit is set and cleared by software.
To write before to set CR[24]=PLLON bit.
0: Center spread
1: Down spread