Figure 16. Clock Tree - STMicroelectronics STM32F405 Reference Manual

Reset and clock control for STM32F42xxx and STM32F43xxx (RCC)
Each clock source can be switched on or off independently when it is not used, to optimize
power consumption.
1. For full details about the internal and external clock source characteristics, refer to the Electrical characteristics section in
the device datasheet.
2. When TIMPRE bit of the RCC_DCKCFGR register is reset, if APBx prescaler is 1, then TIMxCLK = PCLKx, otherwise
TIMxCLK = 2x PCLKx.
3. When TIMPRE bit in the RCC_DCKCFGR register is set, if APBx prescaler is 1,2 or 4, then TIMxCLK = HCLK, otherwise
TIMxCLK = 4x PCLKx.
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Figure 16. Clock tree

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