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1.IIC历史

2.IIC优势

3.IIC时序

3.1 初始化IIC

//初始化IIC
void PCA9557_Init(void)
{					     RCC->APB2ENR |= 1<<4;//先使能外设IO PORTC时钟 							 GPIOC->CRH &= 0XFFFF00FF;//PC10/11 推挽输出GPIOC->CRH |= 0X00003300;	   GPIOC->ODR |= 1<<10;     //PC10 输出高GPIOC->ODR |= 1<<11;     //PC11 输出高
}

3.2 产生IIC起始信号

//产生IIC起始信号
void PCA9557_Start(void)
{PCA9557_SDA_OUT(); //sda线输出PCA9557_SDA=1;PCA9557_SCL=1;delay_us(4);PCA9557_SDA=0;//START:when CLK is high,DATA change form high to lowdelay_us(4);PCA9557_SCL=0;//钳住I2C总线，准备发送或接收数据
}

3.3 产生IIC停止信号

//产生IIC停止信号
void PCA9557_Stop(void)
{PCA9557_SDA_OUT();//sda线输出PCA9557_SCL=0;PCA9557_SDA=0;//STOP:when CLK is high DATA change form low to highdelay_us(4);PCA9557_SCL=1;PCA9557_SDA=1;//发送I2C总线结束信号delay_us(4);
}

3.4 等待ACK

//等待应答信号到来
//返回值：1，接收应答失败
// 0，接收应答成功
uint8_t PCA9557_Wait_Ack(void)
{uint8_t ucErrTime=0;PCA9557_SDA_IN(); //SDA设置为输入PCA9557_SDA=1;delay_us(1);PCA9557_SCL=1;delay_us(1);while(PCA9557_READ_SDA){ucErrTime++;if(ucErrTime>250){PCA9557_Stop();return 1;}}PCA9557_SCL=0;//时钟输出0return 0;
}

3.5 产生ACK / 不产生ACK

//产生ACK应答
void PCA9557_ACK(void)
{PCA9557_SCL=0;PCA9557_SDA_OUT();PCA9557_SDA=0;delay_us(2);PCA9557_SCL=1;delay_us(2);PCA9557_SCL=0;
}//不产生ACK应答
void PCA9557_NAck(void)
{PCA9557_SCL=0;PCA9557_SDA_OUT();PCA9557_SDA=1;delay_us(2);PCA9557_SCL=1;delay_us(2);PCA9557_SCL=0;
}

3.6 IIC发送一个字节

//IIC发送一个字节
//返回从机有无应答
//1，有应答
//0，无应答
uint8_t PCA9557_Send_Byte(uint8_t txd)
{uint8_t t;PCA9557_SDA_OUT();PCA9557_SCL=0;//拉低时钟开始数据传输for(t=0;t<8;t++){if (txd&0x80) PCA9557_SDA = 1;else PCA9557_SDA = 0;txd<<=1;delay_us(2); //对TEA5767这三个延时都是必须的PCA9557_SCL=1;delay_us(2);PCA9557_SCL=0;delay_us(2);}t=PCA9557_Wait_Ack();  //这里固定只要写字节就需要等待应答return (t);
}

3.7 IIC读取一个字节

//读1个字节，ack=1时，发送ACK，ack=0，发送nACK
uint8_t PCA9557_Read_Byte(uint8_t ack)
{uint8_t i,receive=0;PCA9557_SDA_IN();//SDA设置为输入for(i=0;i<8;i++ ){PCA9557_SCL=0;delay_us(2);PCA9557_SCL=1;receive<<=1;if(PCA9557_READ_SDA)receive |= 1;delay_us(1);}if (!ack)PCA9557_NAck();//发送nACKelsePCA9557_ACK(); //发送ACKreturn receive;
}

3.8 IIC发送多字节

uint8_t PCA9557Write(uint8_t addr, uint8_t len, uint8_t *pData)
{uint8_t i;PCA9557_Start();if(PCA9557_Send_Byte(PCA9557_ADDR_WRITE)==1){PCA9557_Stop();return 0;}if(PCA9557_Send_Byte(addr)==1){PCA9557_Stop();return 0;}for(i = 0; i < len; i++){if(PCA9557_Send_Byte(pData[i])==1){PCA9557_Stop();return 0;}}PCA9557_Stop();return 1;
}

3.9 IIC读取多字节

uint8_t PCA9557Read(uint8_t addr,uint8_t len,uint8_t *pData)
{uint8_t i;PCA9557_Start();if(PCA9557_Send_Byte(PCA9557_ADDR_WRITE)==1){PCA9557_Stop();return 0;}if(PCA9557_Send_Byte(addr)==1){PCA9557_Stop();return 0;}PCA9557_Start();if(PCA9557_Send_Byte(PCA9557_ADDR_READ)==1){PCA9557_Stop();return 0;}for(i=0; i<len-1; i++){pData[i] = PCA9557_Read_Byte(1);}pData[len-1] = PCA9557_Read_Byte(0);PCA9557_Stop();return 1;
}

4 IIC问题

4.1 STM32 HAL库的IIC设备地址没有左移

#define I2C_7BIT_ADD_WRITE(__ADDRESS__)                    ((uint8_t)((__ADDRESS__) & (uint8_t)(~I2C_OAR1_ADD0)))
#define I2C_7BIT_ADD_READ(__ADDRESS__)                     ((uint8_t)((__ADDRESS__) | I2C_OAR1_ADD0))

底层中并没有把设备的地址左移，而是直接把最低位改为“0”或“1”，需要自己把器件地址的左移了一位。

	stat = HAL_I2C_Mem_Read(&hi2c1,(PCA9557_I2C_BUS_ADDR << 1),PCA9557_INPUT_REG,1,&io_statu,1,0xFF);if(stat != 0 ){LOG_INFO("io %d Read Error STAT %d\r\n",io,stat);}