前言：本文章部分代码参考自野火的例程

有纰漏请指出，转载请说明。

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1 硬件分析

1.1 GPIOB 基地址

例如：点亮红灯，即GPIOB_5输出低电平

1.2 开启GPIOB所在的APB2的RCC时钟

寄存器偏移地址

1.3 配置GPIOB的CRL寄存器，设置GPIO模式

1.4 配置GPIOB的ODR寄存器，PB5输出低电平

2 软件分析

2.1 直接对寄存器地址赋值

//RCC_APB2ENR bit3置1，即GPIOB端口时钟使能
*(unsigned int*)(0x40021018) |= (1<<3);

//清空GPIOx_CRL 的bit20~bit23            
//*(unsigned int*)(0x40010c00) &= ~( 0x0F<< (4*5)); 

//向GPIOx_CRL 的bit20~bit23 写入3，即PB5以50MHz通用推挽输出 
*(unsigned int*)(0x40010c00) |= (3<<4*5);          

//GPIOx_ODR 的 bit5 置0，即PB5输出低电平
*(unsigned int*)(0x40010c0c) |= ~(0x20);      

2.2 用宏 定义寄存器地址

#define GPIOB_CRL     *(unsigned int*)(0x40010c00)
#define GPIOB_ODR     *(unsigned int*)(0x40010c0c)
#define RCC_APB2ENR   *(unsigned int*)(0x40021018)

//RCC_APB2ENR bit3置1，即GPIOB端口时钟使能
RCC_APB2ENR |= (1<<3);

//清空GPIOx_CRL 的bit20~bit23            
//GPIOB_CRL &= ~( 0x0F<< (4*5)); 

//向GPIOx_CRL 的bit20~bit23 写入3，即PB5以50MHz通用推挽输出 
GPIOB_CRL |= (3<<4*5);          

//GPIOx_ODR 的 bit5 置0，即PB5输出低电平
GPIOB_ODR |= ~(0x20);     

2.3 用固件库方法

/* stm32f10x.h */

#ifndef __STM32F10X_H
#define __STM32F10X_H

#define        PERIPH_BASE              ((unsigned int)0x40000000)
#define        APB1PERIPH_BASE           PERIPH_BASE
#define        APB2PERIPH_BASE          (PERIPH_BASE + 0x10000)
#define        AHBPERIPH_BASE           (PERIPH_BASE + 0x20000)

#define  RCC_BASE                (AHBPERIPH_BASE + 0x1000)
#define  GPIOB_BASE              (APB2PERIPH_BASE + 0x0C00)
#define  RCC_APB2ENR            *(unsigned int*)(RCC_BASE + 0x18)

typedef unsigned int      uint32_t;
typedef unsigned short    uint16_t;

typedef struct
{
    uint32_t CRL;
    uint32_t CRH;
    uint32_t IDR;
    uint32_t ODR;
    uint32_t BSRR;
    uint32_t BRR;
    uint32_t LCKR;
}GPIO_TypeDef;

typedef struct
{
    uint32_t CR;
    uint32_t CFGR;
    uint32_t CIR;
    uint32_t APB2RSTR;
    uint32_t APB1RSTR;
    uint32_t AHBENR;
    uint32_t APB2ENR;
    uint32_t APB1ENR;
    uint32_t BDCR;
    uint32_t CSR;
}RCC_TypeDef;

#define GPIOB   ((GPIO_TypeDef*)GPIOB_BASE)
#define RCC     ((RCC_TypeDef*)RCC_BASE)

/* stm32f10x_gpio.h */

#ifndef __STM32F10X_GPIO_H
#define __STM32F10X_GPIO_H

#include "stm32f10x.h"

#define GPIO_Pin_0    ((uint16_t)0x0001)  /*!< 选择Pin0 */    //(00000000 00000001)b
#define GPIO_Pin_1    ((uint16_t)0x0002)  /*!< 选择Pin1 */    //(00000000 00000010)b
#define GPIO_Pin_2    ((uint16_t)0x0004)  /*!< 选择Pin2 */    //(00000000 00000100)b
#define GPIO_Pin_3    ((uint16_t)0x0008)  /*!< 选择Pin3 */    //(00000000 00001000)b
#define GPIO_Pin_4    ((uint16_t)0x0010)  /*!< 选择Pin4 */    //(00000000 00010000)b
#define GPIO_Pin_5    ((uint16_t)0x0020)  /*!< 选择Pin5 */    //(00000000 00100000)b
#define GPIO_Pin_6    ((uint16_t)0x0040)  /*!< 选择Pin6 */    //(00000000 01000000)b
#define GPIO_Pin_7    ((uint16_t)0x0080)  /*!< 选择Pin7 */    //(00000000 10000000)b
#define GPIO_Pin_8    ((uint16_t)0x0100)  /*!< 选择Pin8 */    //(00000001 00000000)b
#define GPIO_Pin_9    ((uint16_t)0x0200)  /*!< 选择Pin9 */    //(00000010 00000000)b
#define GPIO_Pin_10   ((uint16_t)0x0400)  /*!< 选择Pin10 */   //(00000100 00000000)b
#define GPIO_Pin_11   ((uint16_t)0x0800)  /*!< 选择Pin11 */   //(00001000 00000000)b
#define GPIO_Pin_12   ((uint16_t)0x1000)  /*!< 选择Pin12 */   //(00010000 00000000)b
#define GPIO_Pin_13   ((uint16_t)0x2000)  /*!< 选择Pin13 */   //(00100000 00000000)b
#define GPIO_Pin_14   ((uint16_t)0x4000)  /*!< 选择Pin14 */   //(01000000 00000000)b
#define GPIO_Pin_15   ((uint16_t)0x8000)  /*!< 选择Pin15 */   //(10000000 00000000)b
#define GPIO_Pin_All  ((uint16_t)0xFFFF)  /*!< 选择全部引脚*/ //(11111111 11111111)b

void GPIO_SetBits(GPIO_TypeDef *GPIOx,uint16_t GPIO_Pin);
void GPIO_ResetBits( GPIO_TypeDef *GPIOx,uint16_t GPIO_Pin );

#endif //__STM32F10X_GPIO_H

/* stm32f10x_gpio.c */

#include "stm32f10x_gpio.h"

void GPIO_SetBits(GPIO_TypeDef *GPIOx,uint16_t GPIO_Pin){
    GPIOx->BSRR |= GPIO_Pin;
}
void GPIO_ResetBits(GPIO_TypeDef *GPIOx,uint16_t GPIO_Pin){
    GPIOx->BRR |= GPIO_Pin;
}

/* main.c */

#include "stm32f10x.h" 
#include "stm32f10x_gpio.h" 

int main(void)
{    
    RCC->APB2ENR  |=  ( (1) << 3 );
    GPIOB->CRL |=  ( (3) << (4*1) );
    GPIO_ResetBits(GPIOB,GPIO_Pin_1);
    while(1);
}