The STM32 microcontroller clock tree system consists of five clock sources
The STM32 microcontroller clock tree system consists of five clock sources. Among them,
two are from the internal, as a high-speed and a low-speed. While two clocks can be provided
externally, also with a high-speed and a low-speed, and the fifth one is a PLL clock. Due to the
low accuracy of the on-chip oscillator and its susceptibility to supply and temperature, an
external clock is used in the circuit design, as shown in Figure 4.7. In the software design, the
8M clock is amplified by 9 times to obtain a 72 MHz, and then the MCU working system clock
is initialized to 72MHz.