DocID025202 Rev 7
152/1080
RM0365
Reset and clock control (RCC)
154
Bit 8
TIM1SW:
Timer1 clock source selection
Set and reset by software to select TIM1 clock source.
The bit is writable only when the following conditions occur: clock system = PLL, and AHB
and APB2 subsystem clock not divided respect the clock system.
The bit is reset by hardware when exiting from the previous condition (user must set the bit
again in case of a new switch is required)
0: PCLK2 clock (doubled frequency when prescaled) (default)
1: PLL vco output (running up to 144 MHz)
Bit 7 Reserved, must be kept at reset value.
Bit 6
I2C3SW:
I2C3 clock source selection (STM32F302x6/8 devices only)
This bit is set and cleared by software to select the I2C3 clock source.
0: HSI clock selected as I2C3 clock source (default)
1: SYSCLK clock selected as I2C3 clock
Bit 5
I2C2SW:
I2C2 clock source selection
This bit is set and cleared by software to select the I2C2 clock source.
0: HSI clock selected as I2C2 clock source (default)
1: SYSCLK clock selected as I2C2 clock
Bit 4
I2C1SW:
I2C1 clock source selection
This bit is set and cleared by software to select the I2C1 clock source.
0: HSI clock selected as I2C1 clock source (default)
1: SYSCLK clock selected as I2C1 clock
Bits 3:2 Reserved, must be kept at reset value.
Bits 1:0
USART1SW[1:0]:
USART1 clock source selection
This bit is set and cleared by software to select the USART1 clock source.
00: PCLK selected as USART1 clock source (default)
01: System clock (SYSCLK) selected as USART1 clock
10: LSE clock selected as USART1 clock
11: HSI clock selected as USART1 clock