STM32——I2C外设总线

一、I2C外设简介

• STM32内部集成了硬件I2C收发电路，可以由硬件自动执行时钟生成、起始终止条件生成、应答位收发、数据收发等功能，减轻CPU的负担【对比USART外设是串口通信的的硬件收发器】

• 支持多主机模型}【分为固定多主机和可变多主机，STM32为可变多主机】

• 支持7位/10位地址模式

  • 10位地址模式下，发送的前2个字节为地址，其中前5位是10位寻址的标志位（11110），后10位是地址位

• 支持不同的通讯速度，标准速度(高达100 kHz)，快速(高达400 kHz)

• 支持DMA

• 兼容SMBus协议（主要用于电源管理系统中）

• STM32F103C8T6 硬件I2C资源：I2C1、I2C2

二、I2C框图

• 主要操作控制寄存器（CR），数据寄存器（DR），状态寄存器（SR）

• 引脚设定
  

• 当数据从数据寄存器转到移位寄存器时，就会置状态寄存器TXE为1，表示发送寄存器为空

• 当数据从移位寄存器转到接收寄存器时，就会置状态寄存器RXNE为1，表示接收寄存器非空

• 自身地址寄存器：设定从机地址

• 双地址寄存器：也是设定从机地址

• 比较器：stm32作为从机时有从机地址，会将收到的寻址通过比较器进行判断

三、I2C基本结构

• I2C通信是高位先行
• 使用硬件I2C时，GPIO口的模式为复用开漏输出
• 对于SDA线的GPIO口，可以完成复用开漏输出和复用功能输入，【硬件I2C使用复用开漏模式，软件I2C采用通用开漏模式】
  

四、主机发送

• 起始条件写1，当起始条件发出后自动清零，接口在生成起始条件后自动从从模式切换到主模式
  
• EV5事件修改了SB标志位，也是由硬件自动清零
  
• EV6事件修改ADDR标志位，在主模式下表示地址发送结束
  
• EV8事件修改TXE标志位，此时数据寄存器为空，移位寄存器非空，可以写入新的数据到DR中，该状态表示移位寄存器正在发送数据
• EV8_2事件修改BTF标志位，表示字节发送结束
  
• 停止条件P写1
  

五、主机接收

• 应答位控制寄存器ACK的配置
  
• EV7事件修改RXNE标志位，此时DR寄存器非空，移位寄存器为空

六、I2C的中断请求

七、软件/硬件波形对比

• I2C同步时序对于波形的要求不高，硬件I2C的波形更加标准

八、硬件I2C读写MPU6050

电路设计

关键代码

MPU6050.c

#include "stm32f10x.h"                  // Device header
#include "MPU6050_Reg.h"

#define MPU6050_ADDRESS		0xD0
//等待和超时退出函数
void MPU6050_WaitEvent(I2C_TypeDef* I2Cx, uint32_t I2C_EVENT)
{
    
    
	uint32_t Timeout;
	Timeout = 10000;
	while (I2C_CheckEvent(I2Cx, I2C_EVENT) != SUCCESS)
	{
    
    
		Timeout --;
		if (Timeout == 0)
		{
    
    
			break;
		}
	}
}

//指定地址写
void MPU6050_WriteReg(uint8_t RegAddress, uint8_t Data)
{
    
    
	I2C_GenerateSTART(I2C2, ENABLE);//生成起始条件
	/*非阻塞式函数需要通过状态标志位判断是否完成*/
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_MODE_SELECT);//检查EV5事件
	
	I2C_Send7bitAddress(I2C2, MPU6050_ADDRESS, I2C_Direction_Transmitter);//发送7位地址，读写标志位由第三个参数决定，该函数自带接收应答的过程【接收数据也自带发送应答功能】
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED);//检查EV6事件
	
	I2C_SendData(I2C2, RegAddress);//将数据写入DR寄存器，硬件自动转到移位寄存器
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_BYTE_TRANSMITTING);//检查EV8事件
	
	I2C_SendData(I2C2, Data);
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_BYTE_TRANSMITTED);//检查EV8——2事件
	
	I2C_GenerateSTOP(I2C2, ENABLE);//生成终止条件
}
//指定地址读，先指定地址写，再调用当前地址读
uint8_t MPU6050_ReadReg(uint8_t RegAddress)
{
    
    
	uint8_t Data;
	//指定地址写
	I2C_GenerateSTART(I2C2, ENABLE);
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_MODE_SELECT);
	
	I2C_Send7bitAddress(I2C2, MPU6050_ADDRESS, I2C_Direction_Transmitter);
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_TRANSMITTER_MODE_SELECTED);
	
	I2C_SendData(I2C2, RegAddress);
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_BYTE_TRANSMITTED);
	//当前地址读
	I2C_GenerateSTART(I2C2, ENABLE);//重复起始条件
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_MODE_SELECT);
	
	I2C_Send7bitAddress(I2C2, MPU6050_ADDRESS, I2C_Direction_Receiver);//发送7位地址，读写标志位由第三个参数决定，不是发送则则置1，发送则为0
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_RECEIVER_MODE_SELECTED);//EV6事件
	/*如果只需要接收一个字节，则在EV6事件之后需要ACK置0且配置stop标志位，否则会多读取一个字节
	如果是接收多个字节则直接等待EV7事件，在EV7_1事件之前ACK置0且配置stop标志位为1*/
	I2C_AcknowledgeConfig(I2C2, DISABLE);//配置ACK应答位为0
	I2C_GenerateSTOP(I2C2, ENABLE);//配置停止位
	
	MPU6050_WaitEvent(I2C2, I2C_EVENT_MASTER_BYTE_RECEIVED);//等待EV7事件
	Data = I2C_ReceiveData(I2C2);//将数据读取到DR寄存器，硬件自动转到移位寄存器
	
	I2C_AcknowledgeConfig(I2C2, ENABLE);//恢复ACK应答位为1，方便指定地址收多个字节
	
	return Data;
}
//硬件I2C初始化和指定地址写
void MPU6050_Init(void)
{
    
    
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_I2C2, ENABLE);
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
	
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_OD;
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10 | GPIO_Pin_11;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOB, &GPIO_InitStructure);
	
	//I2C初始化
	I2C_InitTypeDef I2C_InitStructure;
	I2C_InitStructure.I2C_Mode = I2C_Mode_I2C;
	I2C_InitStructure.I2C_ClockSpeed = 50000;//最大400KHz
	I2C_InitStructure.I2C_DutyCycle = I2C_DutyCycle_2;
	/*在标准速度下占空比为1:1，在快速模式下设置才有用，有2个参数可以选择，
	低电平：高电平分别是16:9和2:1，因为在scl低电平时sda会切换电平，
	此时适当多分配低电平时间可以在快速模式下完成电平变化。*/
	I2C_InitStructure.I2C_Ack = I2C_Ack_Enable;//配置ack应答位
	I2C_InitStructure.I2C_AcknowledgedAddress = I2C_AcknowledgedAddress_7bit;//stm32作为从机可以响应多少位地址
	I2C_InitStructure.I2C_OwnAddress1 = 0x00;//作为从机时设置自身地址1
	I2C_Init(I2C2, &I2C_InitStructure);
	
	I2C_Cmd(I2C2, ENABLE);
	
	MPU6050_WriteReg(MPU6050_PWR_MGMT_1, 0x01);
	MPU6050_WriteReg(MPU6050_PWR_MGMT_2, 0x00);
	MPU6050_WriteReg(MPU6050_SMPLRT_DIV, 0x09);
	MPU6050_WriteReg(MPU6050_CONFIG, 0x06);
	MPU6050_WriteReg(MPU6050_GYRO_CONFIG, 0x18);
	MPU6050_WriteReg(MPU6050_ACCEL_CONFIG, 0x18);
}

uint8_t MPU6050_GetID(void)
{
    
    
	return MPU6050_ReadReg(MPU6050_WHO_AM_I);
}
//获取数据寄存器函数，参数为指针，指向各个数据寄存器的地址
void MPU6050_GetData(int16_t *AccX, int16_t *AccY, int16_t *AccZ, 
						int16_t *GyroX, int16_t *GyroY, int16_t *GyroZ)
{
    
    
	uint8_t DataH, DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_ACCEL_XOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_ACCEL_XOUT_L);
	*AccX = (DataH << 8) | DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_ACCEL_YOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_ACCEL_YOUT_L);
	*AccY = (DataH << 8) | DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_ACCEL_ZOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_ACCEL_ZOUT_L);
	*AccZ = (DataH << 8) | DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_GYRO_XOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_GYRO_XOUT_L);
	*GyroX = (DataH << 8) | DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_GYRO_YOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_GYRO_YOUT_L);
	*GyroY = (DataH << 8) | DataL;
	
	DataH = MPU6050_ReadReg(MPU6050_GYRO_ZOUT_H);
	DataL = MPU6050_ReadReg(MPU6050_GYRO_ZOUT_L);
	*GyroZ = (DataH << 8) | DataL;
}

MPU6050.h

#ifndef __MPU6050_H
#define __MPU6050_H

void MPU6050_WriteReg(uint8_t RegAddress, uint8_t Data);
uint8_t MPU6050_ReadReg(uint8_t RegAddress);

void MPU6050_Init(void);
uint8_t MPU6050_GetID(void);
void MPU6050_GetData(int16_t *AccX, int16_t *AccY, int16_t *AccZ, 
						int16_t *GyroX, int16_t *GyroY, int16_t *GyroZ);

#endif

MPU6050_Reg.h
使用宏定义，将寄存器地址用一个字符串表示

#ifndef __MPU6050_REG_H
#define __MPU6050_REG_H

#define	MPU6050_SMPLRT_DIV		0x19
#define	MPU6050_CONFIG			0x1A
#define	MPU6050_GYRO_CONFIG		0x1B
#define	MPU6050_ACCEL_CONFIG	0x1C

#define	MPU6050_ACCEL_XOUT_H	0x3B
#define	MPU6050_ACCEL_XOUT_L	0x3C
#define	MPU6050_ACCEL_YOUT_H	0x3D
#define	MPU6050_ACCEL_YOUT_L	0x3E
#define	MPU6050_ACCEL_ZOUT_H	0x3F
#define	MPU6050_ACCEL_ZOUT_L	0x40
#define	MPU6050_TEMP_OUT_H		0x41
#define	MPU6050_TEMP_OUT_L		0x42
#define	MPU6050_GYRO_XOUT_H		0x43
#define	MPU6050_GYRO_XOUT_L		0x44
#define	MPU6050_GYRO_YOUT_H		0x45
#define	MPU6050_GYRO_YOUT_L		0x46
#define	MPU6050_GYRO_ZOUT_H		0x47
#define	MPU6050_GYRO_ZOUT_L		0x48

#define	MPU6050_PWR_MGMT_1		0x6B
#define	MPU6050_PWR_MGMT_2		0x6C
#define	MPU6050_WHO_AM_I		0x75

#endif

main.c

#include "stm32f10x.h"                  // Device header
#include "Delay.h"
#include "OLED.h"
#include "MPU6050.h"

uint8_t ID;
int16_t AX, AY, AZ, GX, GY, GZ;

int main(void)
{
    
    
	OLED_Init();
	MPU6050_Init();
	
	OLED_ShowString(1, 1, "ID:");
	ID = MPU6050_GetID();
	OLED_ShowHexNum(1, 4, ID, 2);
	
	while (1)
	{
    
    
		MPU6050_GetData(&AX, &AY, &AZ, &GX, &GY, &GZ);
		OLED_ShowSignedNum(2, 1, AX, 5);
		OLED_ShowSignedNum(3, 1, AY, 5);
		OLED_ShowSignedNum(4, 1, AZ, 5);
		OLED_ShowSignedNum(2, 8, GX, 5);
		OLED_ShowSignedNum(3, 8, GY, 5);
		OLED_ShowSignedNum(4, 8, GZ, 5);
	}
}

状态监控函数

EV事件可以表示多个标志位的状态，采用如下三种方式可以获取状态标志位，常用的方式是第一种，可以读取多个标志位

/**
 * @brief
 ****************************************************************************************
 *
 *                         I2C State Monitoring Functions
 *                       
 ****************************************************************************************   
 * This I2C driver provides three different ways for I2C state monitoring
 *  depending on the application requirements and constraints:
 *        
 *  
 * 1) Basic state monitoring:
 *    Using I2C_CheckEvent() function:
 *    It compares the status registers (SR1 and SR2) content to a given event
 *    (can be the combination of one or more flags).
 *    It returns SUCCESS if the current status includes the given flags 
 *    and returns ERROR if one or more flags are missing in the current status.
 *    - When to use:
 *      - This function is suitable for most applications as well as for startup 
 *      activity since the events are fully described in the product reference manual 
 *      (RM0008).
 *      - It is also suitable for users who need to define their own events.
 *    - Limitations:
 *      - If an error occurs (ie. error flags are set besides to the monitored flags),
 *        the I2C_CheckEvent() function may return SUCCESS despite the communication
 *        hold or corrupted real state. 
 *        In this case, it is advised to use error interrupts to monitor the error
 *        events and handle them in the interrupt IRQ handler.
 *        
 *        @note 
 *        For error management, it is advised to use the following functions:
 *          - I2C_ITConfig() to configure and enable the error interrupts (I2C_IT_ERR).
 *          - I2Cx_ER_IRQHandler() which is called when the error interrupt occurs.
 *            Where x is the peripheral instance (I2C1, I2C2 ...)
 *          - I2C_GetFlagStatus() or I2C_GetITStatus() to be called into I2Cx_ER_IRQHandler()
 *            in order to determine which error occurred.
 *          - I2C_ClearFlag() or I2C_ClearITPendingBit() and/or I2C_SoftwareResetCmd()
 *            and/or I2C_GenerateStop() in order to clear the error flag and source,
 *            and return to correct communication status.
 *            
 *
 *  2) Advanced state monitoring:
 *     Using the function I2C_GetLastEvent() which returns the image of both status 
 *     registers in a single word (uint32_t) (Status Register 2 value is shifted left 
 *     by 16 bits and concatenated to Status Register 1).
 *     - When to use:
 *       - This function is suitable for the same applications above but it allows to
 *         overcome the limitations of I2C_GetFlagStatus() function (see below).
 *         The returned value could be compared to events already defined in the 
 *         library (stm32f10x_i2c.h) or to custom values defined by user.
 *       - This function is suitable when multiple flags are monitored at the same time.
 *       - At the opposite of I2C_CheckEvent() function, this function allows user to
 *         choose when an event is accepted (when all events flags are set and no 
 *         other flags are set or just when the needed flags are set like 
 *         I2C_CheckEvent() function).
 *     - Limitations:
 *       - User may need to define his own events.
 *       - Same remark concerning the error management is applicable for this 
 *         function if user decides to check only regular communication flags (and 
 *         ignores error flags).
 *     
 *
 *  3) Flag-based state monitoring:
 *     Using the function I2C_GetFlagStatus() which simply returns the status of 
 *     one single flag (ie. I2C_FLAG_RXNE ...). 
 *     - When to use:
 *        - This function could be used for specific applications or in debug phase.
 *        - It is suitable when only one flag checking is needed (most I2C events 
 *          are monitored through multiple flags).
 *     - Limitations: 
 *        - When calling this function, the Status register is accessed. Some flags are
 *          cleared when the status register is accessed. So checking the status
 *          of one Flag, may clear other ones.
 *        - Function may need to be called twice or more in order to monitor one 
 *          single event.
 *            
 */

/**
 * 
 *  1) Basic state monitoring
 *******************************************************************************
 */
ErrorStatus I2C_CheckEvent(I2C_TypeDef* I2Cx, uint32_t I2C_EVENT);
/**
 * 
 *  2) Advanced state monitoring
 *******************************************************************************
 */
uint32_t I2C_GetLastEvent(I2C_TypeDef* I2Cx);
/**
 * 
 *  3) Flag-based state monitoring
 *******************************************************************************
 */
FlagStatus I2C_GetFlagStatus(I2C_TypeDef* I2Cx, uint32_t I2C_FLAG);
/**
 *
 *******************************************************************************
 */

void I2C_ClearFlag(I2C_TypeDef* I2Cx, uint32_t I2C_FLAG);
ITStatus I2C_GetITStatus(I2C_TypeDef* I2Cx, uint32_t I2C_IT);
void I2C_ClearITPendingBit(I2C_TypeDef* I2Cx, uint32_t I2C_IT);

#ifdef __cplusplus
}
#endif

参考视频：江科大自化协