
RM0008
Connectivity line devices: reset and clock control (RCC)
Doc ID 13902 Rev 12
133/1096
Bits 14:14
ADCPRE[1:0]
: ADC prescaler
Set and cleared by software to select the frequency of the clock to the ADCs.
00: PCLK2 divided by 2
01: PCLK2 divided by 4
10: PCLK2 divided by 6
11: PCLK2 divided by 8
Bits 13:11
PPRE2[2:0]
: APB high-speed prescaler (APB2)
Set and cleared by software to control the division factor of the APB High speed clock (PCLK2).
0xx: HCLK not divided
100: HCLK divided by 2
101: HCLK divided by 4
110: HCLK divided by 8
111: HCLK divided by 16
Bits 10:8
PPRE1[2:0]
: APB Low-speed prescaler (APB1)
Set and cleared by software to control the division factor of the APB Low speed clock (PCLK1).
0xx: HCLK not divided
100: HCLK divided by 2
101: HCLK divided by 4
110: HCLK divided by 8
111: HCLK divided by 16
Caution:
Software must configure these bits ensure that the frequency in this domain does not
exceed 36 MHz.
Bits 7:4
HPRE[3:0]
: AHB prescaler
Set and cleared by software to control AHB clock division factor.
0xxx: SYSCLK not divided
1000: SYSCLK divided by 2
1001: SYSCLK divided by 4
1010: SYSCLK divided by 8
1011: SYSCLK divided by 16
1100: SYSCLK divided by 64
1101: SYSCLK divided by 128
1110: SYSCLK divided by 256
1111: SYSCLK divided by 512
Note: The prefetch buffer must be kept on when using a prescaler different from 1 on the AHB clock.
Refer to the section
Reading the Flash memory on page 58
Caution:
The AHB clock frequency must be at least 25 MHz when the Ethernet is used.
Bits 3:2
SWS[1:0]
: System clock switch status
Set and cleared by hardware to indicate which clock source is used as system clock.
00: HSI oscillator used as system clock
01: HSE oscillator used as system clock
10: PLL used as system clock
11: Not applicable