3.3 Clock configuration of stM32 In general, an embedded system should be initialized before it works In embedded system initialization, the system should be set up. The clock source should be considered in clock setup and PLL Should also be considered then the internal bus external bus and peripherals clock should be set up. The flow chart of clock setup is shown in Fig 3-1 Enable hse clock Set up AB clock according to the system clock RCC HCLK Config Set up APB2 clock according to AHB clock RCC HCLK2 Config Set up aPbl clock according to AHB clock RCC HCLKIConfig Select HIS, HSE or PLL as the system Set up system clock clock Enable peripherals ig. 3-1 Flow chart of clock setup RCC AHBPeriphClock Cmd11 In general, an embedded system should be initialized before it works. In embedded system initialization, the system should be set up. The clock source should be considered in clock setup, and PLL should also be considered. Then the internal bus, external bus and peripherals clock should be set up. The flow chart of clock setup is shown in Fig.3-1. 3.3 Clock configuration of STM32 Enable HSE clock Set up AHB clock according to the system clock RCC_HCLKConfig Set up APB2 clock according to AHB clock RCC_HCLK2Config Set up APB1 clock according to AHB clock RCC_HCLK1Config Set up system clock Enable peripherals RCC_AHBPeriphClockCmd Select HIS, HSE or PLL as the system clock Fig. 3-1 Flow chart of clock setup