#include <reg52.h>
#include <intrins.h>
#include "I2C.h"
#define I2CDelay() {_nop_();_nop_();_nop_();_nop_();}
/* 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; //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; //先拉高SCL
I2CDelay();
I2C_SDA = 1; //再拉高SDA
I2CDelay();
}
/* I2C总线写操作,dat-待写入字节,返回值-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的掩码变量
for (mask=0x80; mask!=0; mask>>=1) //从高位到低位依次进行
{
I2C_SDA=1;
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,即为从机的应答值
I2CDelay();
I2C_SCL = 0; //再拉低SCL完成应答位,并保持住总线
return (~ack); //应答值取反以符合通常的逻辑:
//0=不存在或忙或写入失败,1=存在且空闲或写入成功
}
/* I2C总线读操作,并发送非应答信号,返回值-读到的字节 */
unsigned char I2CReadNAK()
{
unsigned char mask;
unsigned char dat;
I2C_SDA = 1; //首先确保主机释放SDA
for (mask=0x80; mask!=0; mask>>=1) //从高位到低位依次进行
{
I2CDelay();
I2C_SCL = 1; //拉高SCL
I2C_SDA=1;
if(I2C_SDA == 0) //读取SDA的值
dat &= ~mask; //为0时,dat中对应位清零
else
dat |= mask; //为1时,dat中对应位置1
I2CDelay();
I2C_SCL = 0; //再拉低SCL,以使从机发送出下一位
}
I2C_SDA = 1; //8位数据发送完后,拉高SDA,发送非应答信号
I2CDelay();
I2C_SCL = 1; //拉高SCL
I2CDelay();
I2C_SCL = 0; //再拉低SCL完成非应答位,并保持住总线
return dat;
}
/* I2C总线读操作,并发送应答信号,返回值-读到的字节 */
unsigned char I2CReadACK()
{
unsigned char mask;
unsigned char dat;
I2C_SDA = 1; //首先确保主机释放SDA
for (mask=0x80; mask!=0; mask>>=1) //从高位到低位依次进行
{
I2CDelay();
I2C_SCL = 1; //拉高SCL
if(I2C_SDA == 0) //读取SDA的值
dat &= ~mask; //为0时,dat中对应位清零
else
dat |= mask; //为1时,dat中对应位置1
I2CDelay();
I2C_SCL = 0; //再拉低SCL,以使从机发送出下一位
}
I2C_SDA = 0; //8位数据发送完后,拉低SDA,发送应答信号
I2CDelay();
I2C_SCL = 1; //拉高SCL
I2CDelay();
I2C_SCL = 0; //再拉低SCL完成应答位,并保持住总线
return dat;
}