Use stm32 to light a lamp [operation register + library function]

The use of stm32 is different from that of 51 microcontroller. The microcontroller can directly operate the io port by connecting the crystal oscillator and the power supply, but the clock of stm32 is

After being amplified by the frequency multiplier, the phase-locked loop outputs a stable clock frequency.

Doing so brings many benefits. Although the external clock of stm32 is only 8Mhz, after passing through the frequency multiplier, several clock frequencies can be obtained to provide different clock frequencies for different peripherals.

Therefore, STM32 has many buses, the frequencies of these buses are different, and the buses are closed before use. The corresponding buses must be opened before using the peripherals. This is also for the consideration of reducing power consumption for STM32.

All peripherals using stm32 must add their corresponding driver files.   

One thing to note about the GPIO port of stm32 is that the GPIO port can be configured into 8 working modes through the GPIO register:

• Floating Input                                         

• Input with pull-up resistor

• Input with pull-down resistor

• Analog Input

• Open-drain output

• Push-pull output

• Multiplexed push-pull output

• Multiplexed open-drain output

The first four are input states:

With pull-up resistor means that the stm32 has a pull-up resistor inside, and the same applies to pull-down.

Floating input means that there is nothing connected inside the stm32, and you need to connect an external pull-up resistor;

Analog input is used for AD conversion.

The last four are output states:

Open-drain output means that it can output a low level, but if you want to output a high level, you need a pull-up resistor;

Push-pull output means that it can output both high level and low level;

The last two are to open the second function of IO, and they need to be configured to this state when IO port is multiplexed.

This article will implement the LED cyclic flashing on the GPIOA_Pin_4 port.

Operation Register

Each I/O port of stm32 can be freely programmed, and the register of a single I/O port must be accessed as a 32-bit word. Each I/O port of stm32 is controlled by 7 registers:

• The two 32-bit port configuration registers CRL (low eight-bit I/O port configuration register) and CRH (high eight-bit I/O port configuration register) in the configuration mode control the mode and output rate of each I/O port.

    Description of each bit of CRL output register (same as CRH):

    The reset value of this register is 0X4444 4444, which means the port is configured to floating input mode. Each I/O port occupies four configuration bits, the upper two bits are CNF, which sets the input and output mode. The lower two bits are Mode, which sets the output rate.

• There are two 32-bit data registers, IDR and ODR, but only the lower 16 bits are used and can only be read in 16-bit form. The ODR register can be used to select the resistor pull-up (corresponding position 1) or pull-down mode for each I/O port in input mode; or to set the output level of each I/O port in output mode;

     Description of each bit of ODR output register (same as IRH):

• 1 32-bit set/reset register BSRR;

• 1 16-bit reset register BRR;

• 1 32-bit latch register LCKR;

The clock of the GPIO port is on the APB2 bus. Change the description of each bit of the clock bus register APB2ENR to:

Register operation method code: (sys.h code refers to the  stm32 direct operation register development environment configuration )

#include 	   
#include "system.h"		


//LED port definition

#define LED0 PAout(4) // PA4

void Gpio_Init(void);		   

int main(void)
{				  
	Rcc_Init(9); //System clock settings
	Gpio_Init(); //Initialize the hardware interface connected to the LED
	while(1)
	{
		LED0=0;
		delay(300000); //delay 300ms
		LED0=1;
		delay(300000);
	}	 
}


void Gpio_Init(void)
{
	RCC->APB2ENR|=1<<2; //Enable PORTA clock	   	 
	   	 
	GPIOA->CRL&=0XFFF0FFFF; 
	GPIOA->CRL|=0X00030000; //PA4 push-pull output   	 
        GPIOA->ODR|=1<<4; //PA4 output high
	  
}

Library function operation

Even if you want to light up an LED, you must first configure the stm32 clock and open the corresponding bus. Before writing the corresponding code, you need to add the peripheral driver files used to the MDK project. You need to add the general io port driver stm32f10x_gpio.c and the clock driver stm32f10x_rcc.c to the project. These two files are under Libraries/src  

After adding Keil, it looks like this: 

code show as below:  

#include "stm32f10x.h"

void RCC_Configuration(void);
void GPIO_Configuration(void);
void delay(vu32 n); //delay function

int main(void)
{
  	RCC_Configuration();
	GPIO_Configuration();

	while(1){

		GPIO_SetBits(GPIOA,GPIO_Pin_4); //Call library function to set LED_1 to 1 and output high level

		delay(2000000);


		GPIO_ResetBits(GPIOA,GPIO_Pin_4);		

		delay(2000000);
	}
}

void GPIO_Configuration(void)
{
	GPIO_InitTypeDef GPIO_InitStructure; //Structure initialization

  	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
 	GPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz; 
  	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;	
  	GPIO_Init(GPIOA, &GPIO_InitStructure); 

}

void delay(vu32 n)
{
 	while(--n);
}


void RCC_Configuration(void)
{
	/* Define enumeration type variable HSEStartUpStatus */
	ErrorStatus HSEStartUpStatus;

  	/* Reset system clock settings */
  	RCC_DeInit();
  	/* Enable HSE*/
  	RCC_HSEConfig(RCC_HSE_ON);
  	/* Wait for HSE to start oscillating and stabilize*/
  	HSEStartUpStatus = RCC_WaitForHSEStartUp();
	/* Determine whether the HSE is successfully started, if yes, enter if() */
  	if(HSESTartUpStatus == SUCCESS)
  	{
    	/* Select HCLK (AHB) clock source as SYSCLK divided by 1 */
    	RCC_HCLKConfig(RCC_SYSCLK_Div1); 
    	/* Select PCLK2 clock source as HCLK (AHB) divided by 1 */
    	RCC_PCLK2Config(RCC_HCLK_Div1); 
    	/* Select PCLK1 clock source as HCLK (AHB) divided by 2 */
    	RCC_PCLK1Config(RCC_HCLK_Div2);
    	/* Set the FLASH delay cycle number to 2 */
    	//FLASH_SetLatency(FLASH_Latency_2);
    	/* Enable FLASH prefetch cache */
    	//FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
    	/* Select the phase-locked loop (PLL) clock source as HSE 1 division, the multiplier is 9, then the PLL output frequency is 8MHz * 9 = 72MHz */
    	RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);
    	/* Enable PLL */ 
    	RCC_PLLCmd(ENABLE);
    	/* Wait for PLL output to stabilize */
    	while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET);
    	/* Select SYSCLK clock source as PLL */
    	RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
    	/* Wait for PLL to become the SYSCLK clock source */
    	while(RCC_GetSYSCLKSource() != 0x08);
  	} 


  	/* Turn on the GPIOA clock on the APB2 bus */
  	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);		
	
}