#define I2CDelay() {_nop_();_nop_();_nop_();_nop_();}
sbit I2C_SCL = P3^7;
sbit I2C_SDA = P3^6;


/*产生总线起始信号*/
void I2CStart()
{
	I2C_SDA = 1;							//首先确保SDA,SCL都是高电平
	I2C_SCL = 1;
	I2CDelay();
	I2C_SDA = 0; 							//首先拉低SDA
	I2CDelay();
	I2C_SCL = 0;							//再拉低SCL
}

/*产生总线停止信号*/
void I2CStop()
{
	I2C_SCL = 0;							//首先确保SDA,SCL都是低电平
	I2C_SDA = 0;
	I2CDelay();
	I2C_SCL = 1; 							//首先拉高SCL
	I2CDelay();
	I2C_SDA = 1;							//再拉高SDA
	I2CDelay();
}
/*I2C总线写操作，dat为待写入字节，返回值为从机应答位的值*/
bit I2CWrite(unsigned char dat)
{
	bit ack;		   						//用于暂存应答位的值
	unsigned char mask;						//用于探测字节内某一位值得掩码变量

	for(mask = 0x80; mask != 0; mask >>= 1)	//从高位到低位一次进行
	{
		if((mask & dat) == 0)				//该位的值输出到SDA上
			I2C_SDA = 0;
		else
			I2C_SDA = 1;
		I2CDelay();
		I2C_SCL = 1;  						//拉高SCL
		I2CDelay();
		I2C_SCL = 0;						//再拉低SCL，完成一个位周期
	}

	I2C_SDA = 1;   							//8位数据发送完成后，主机释放SDA，以检测从机应答
	I2CDelay();
	I2C_SCL = 1;  							//拉高SCL
	ack = I2C_SDA;							//读取此时的SDA值，既为从机的应答位
	I2CDelay();
	I2C_SCL = 0;							//再次拉低SCL完成应答位，并保持住总线

	return ack;								//返回从机应答值
}
/*I2C总线读操作*/
unsigned char  I2CRead(bit ack)
{
	unsigned char mask;
	unsigned char dat;

	I2C_SDA = 1;
	for(mask = 0x80; mask != 0; mask >>= 1)
	{
		I2CDelay();
		I2C_SCL = 1;
		if(I2C_SDA == 0)
			dat &= ~mask;
		else
			dat |= mask;
		I2CDelay();
		I2C_SCL = 0;
	}
	I2C_SDA = ~ ack;
	I2CDelay();
	I2C_SCL = 1;
	I2CDelay();
	I2C_SCL = 0;

	return dat;
}

此代码为学习《手把手教你学51单片机》后编写