Stm32 clock Configuration

In stm32, there are five clock sources:HSI,HSE,LSI,LSE,PLL.

①HSIIt is a high-speed internal clock, RC oscillator, and the frequency is 8 MHz.

②HSEIt is a high-speed external clock, which can be connected to a Z/Ceramic Resonator or an external clock source. The frequency range is 4 MHz ~ 16 MHz.

③LSIIt is a low-speed internal clock, RC oscillator, and the frequency is 40 kHz.

④LSEIt is a Z crystal with a low-speed external clock and a connection frequency of 32.768khz.

⑤PLLThe clock input source can be HSI/2, HSE or HSE/2. The multiplier value can be 2 ~ 16 times, but its output frequency cannot exceed 72 MHz.

 

InStm32If the external crystal oscillator is not used,Osc_inAndOsc_outMethod

If you use an internal RC oscillator instead of an external crystal oscillator, follow these steps:

1) for products with 100 or 144 feet, osc_in should be grounded and osc_out should be suspended. 2) for products with less than 100 feet, there are two methods: 2.1) osc_in and osc_out are grounded by a 10 k resistor respectively. This method improves EMC performance. 2.2) remap osc_in and osc_out to pd0 and pd1 respectively, and configure pd0 and pd1 as the push-pull output and output '0 '.

Use HSE clock,ProgramSet the clock parameters:

1. Reset the RCC register to the default rcc_deinit;

2. Enable the external high-speed clock crystal oscillator HSE rcc_hseconfig (rcc_hse_on );

3. Wait for the external high-speed clock crystal oscillator to work hsestartupstatus = rcc_waitforhsestartup ();

4. Set the AHB clock rcc_hclkconfig;

5. Set the high-speed AHB clock rcc_pclk2config;

6. Set the low-speed AHB clock rcc_pclk1config;

7. Set PLL rcc_pllconfig;

8. Enable PLL rcc_pllcmd (enable );

9. Wait for the PLL to work while (rcc_getflagstatus (rcc_flag_pllrdy) = reset)

10. Set the system clock rcc_sysclkconfig;

11. Determine if the PLL is a system clock while (rcc_getsysclksource ()! = 0x08)

12. Enable the peripheral clock rcc_apb2periphclockcmd ()/rcc_apb1periphclockcmd ()

 

 

The following is the RCC configuration function in the tm32 software Firmware Library (using an external 8 MHz Crystal Oscillator)

  /* **************************************** * ************************************ Function name: rcc_configuration * Description: RCC configuration (using an external 8 MHz Crystal Oscillator) * input: none * output: none * return: no *************************************** ***************************************  */  Void Rcc_configuration ( Void  ){  /*  Reset the peripheral RCC register to the default value  */  Rcc_deinit ();  /*  Set external high-speed crystal oscillator (HSE)  */ Rcc_hseconfig (rcc_hse_on );  //  RCC_HSE_ON--HSE crystal open (on)     /*  Wait for HSE to start  */  Hsestartupstatus = Rcc_waitforhsestartup ();  If (Hsestartupstatus = success) //  Success: HSE crystal oscillator stable and ready  {  /*  Set the AHB clock (hclk)  */ Rcc_hclkconfig (rcc_sysclk_div1 );  //  Rcc_sysclk_div1 -- AHB clock = system clock       /*  Set high-speed AHB clock (pclk2)  */  Rcc_pclk2config (rcc_hclk_div1 );  //  Rcc_hclk_div1 -- apb2 clock = hclk       /*  Set low-speed AHB clock (pclk1)  */  Rcc_pclk1config (rcc_hclk_div2 );  // Rcc_hclk_div2 -- apb1 clock = hclk/2      /*  Set the delay time period of flash memory  */  Flash_setlatency (flash_latency_2 );  //  Flash_latency_2 delay period    /*  Select the cache mode for flash prefetch.  */  Flash_prefetchbuffercmd (flash_prefetchbuffer_enable );  //  Prefetch refers to cache enabling       /*  Set the PLL clock source and frequency doubling factor */  Rcc_pllconfig (rcc_pllsource_hse_div1, rcc_pllmul_9 );  //  PLL input clock = HSE clock frequency; rcc_pllmul_9 -- PLL input clock x 9    /*  Enable PLL  */  Rcc_pllcmd (enable );  /*  Check whether the specified RCC flag (PLL ready flag) is set.  */        While (Rcc_getflagstatus (rcc_flag_pllrdy) = Reset ){}  /* Set the system clock (sysclk)  */  Rcc_sysclkconfig (rcc_sysclksource_pllclk );  //  Rcc_sysclksource_pllclk -- select PLL as the system clock      /*  The PLL returns the clock source used as the system clock.  */      While (Rcc_getsysclksource ()! = 0x08 ) //  0x08: PLL as the system clock  {}}  /* Enable or disable apb2 peripheral clock  */  Rcc_apb2periphclockcmd (rcc_apb2periph_gpioa | Rcc_apb2periph_gpiob | Rcc_apb2periph_gpioc, enable );  //  Rcc_apb2periph_gpioa gpioa clock  //  Rcc_apb2periph_gpiob gpiob clock  //  Rcc_apb2periph_gpioc gpioc clock  //  Rcc_apb2periph_gpiod gpiod clock  }