*     51系列单片机在使用时，有时需要模拟I2C总线，                      */
/*   这里举出一个实例（读写串行EEPROM芯片at2402）                       */
/************************************************************************/
/* Name:AT24C02存储器的读写程序,用到I2C总线,含相对独立的I2C总线读写函数 */
/* Language: C51单片机编程语言                                          */
/* Platform: Win98,Intel Celeron 433 Processor,伟福仿真器，仿真8751     */
/* Date: 2003年5月21日,5月22日,5月29日                                  */
/* Version: 1.1.1                            */
/* Others: None                                                         */
/************************************************************************/

    #include<string.h>
    #include<reg52.h>
    #include<intrins.h>
    #define DELAY_TIME 60 /*经实验，不要小于50！否则可能造成时序混乱*/
    #define TRUE 1
    #define FALSE 0

    sbit SCL=P1^7;/*假设由P1.7和P1.6控制*/
    sbit SDA=P1^6;

/********** Function Definition　函数定义 ************/

    void DELAY(unsigned int t) /*延时函数*/
    {
        while(t!=0)
            t--;
    }

    void I2C_Start(void)
    {
        /*启动I2C总线的函数，当SCL为高电平时使SDA产生一个负跳变*/
        SDA=1;
        SCL=1;
        DELAY(DELAY_TIME);
        SDA=0;
        DELAY(DELAY_TIME);
        SCL=0;
        DELAY(DELAY_TIME);
    }

    void I2C_Stop(void)
    {
        /*终止I2C总线，当SCL为高电平时使SDA产生一个正跳变*/
        SDA=0;
        SCL=1;
        DELAY(DELAY_TIME);
        SDA=1;
        DELAY(DELAY_TIME);
        SCL=0;
        DELAY(DELAY_TIME);
    }

    void SEND_0(void)   /* SEND ACK */
    {
        /*发送0，在SCL为高电平时使SDA信号为低*/
        SDA=0;
        SCL=1;
        DELAY(DELAY_TIME);
        SCL=0;
        DELAY(DELAY_TIME);
    }

    void SEND_1(void)
    {
        /*发送1，在SCL为高电平时使SDA信号为高*/
        SDA=1;
        SCL=1;
        DELAY(DELAY_TIME);
        SCL=0;
        DELAY(DELAY_TIME);
    }

    bit Check_Acknowledge(void)
    {
        /*发送完一个字节后检验设备的应答信号*/
        SDA=1;
        SCL=1;
        DELAY(DELAY_TIME/2);
        F0=SDA;
        DELAY(DELAY_TIME/2);
        SCL=0;
        DELAY(DELAY_TIME);
        if(F0==1)
            return FALSE;
        return TRUE;
    }

    void WriteI2CByte(char b)reentrant
    {
        /*向I2C总线写一个字节*/
        char i;
        for(i=0;i<8;i++)
            if((b<<i)&0x80)
                SEND_1();
            else
                SEND_0();
    }

 

    char ReadI2CByte(void)reentrant
    {
        /*从I2C总线读一个字节*/
        char b=0,i;
        for(i=0;i<8;i++)
        {
            SDA=1;    /*释放总线*/
            SCL=1;    /*接受数据*/
            DELAY(10);
            F0=SDA;
            DELAY(10);
            SCL=0;
            if(F0==1)
                {
                    b=b<<1;
                    b=b|0x01;
                }
            else
                b=b<<1;
        }
        return b;
    }

/**********以下为读写24c02的函数**********/
void Write_One_Byte(char addr,char thedata)
{
          bit acktemp=1;
          /*write a byte to mem*/
          I2C_Start();
          WriteI2CByte(0xa0);
          acktemp=Check_Acknowledge();
          WriteI2CByte(addr);/*address*/
          acktemp=Check_Acknowledge();
          WriteI2CByte(thedata);/*thedata*/
          acktemp=Check_Acknowledge();
          I2C_Stop();

}

void Write_A_Page(char *buffer,char addr)
{
          bit acktemp=1;
          bit wrtmp;
          int i;
          /*write a page to at24c02*/
          I2C_Start();
          WriteI2CByte(0xa0);
          acktemp=Check_Acknowledge();
          WriteI2CByte(addr);/*address*/
          acktemp=Check_Acknowledge();
          for(i=0;i<7;i++)
          {
            WriteI2CByte(buffer[i]);
            if(!Check_Acknowledge())
                {
                    I2C_Stop();

                }
           }

          I2C_Stop();

 

}

char Read_One_Byte(char addr)
{         bit acktemp=1;
          char mydata;
           /*read a byte from mem*/
          I2C_Start();
          WriteI2CByte(0xa0);
          acktemp=Check_Acknowledge();
          WriteI2CByte(addr);/*address*/
          acktemp=Check_Acknowledge();
          I2C_Start();
          WriteI2CByte(0xa1);
          acktemp=Check_Acknowledge();

          mydata=ReadI2CByte();
          acktemp=Check_Acknowledge();

          return mydata;
          I2C_Stop();
}

void Read_N_Bytes(char *buffer,char n,char addr)
{
          bit acktemp=1;

          int i=0;
           /*read 8 bytes from mem*/
          I2C_Start();
          WriteI2CByte(0xa0);
          acktemp=Check_Acknowledge();
          WriteI2CByte(addr);/*address*/
          acktemp=Check_Acknowledge();
          I2C_Start();
          WriteI2CByte(0xa1);

          acktemp=Check_Acknowledge();

 

          for(i=0;i<n;i++)
          {
                buffer[i]=ReadI2CByte();
                if(i!=n-1)
                    SEND_0();    /*发送应答*/
                else
                    SEND_1();    /*发送非应答*/
          }

   I2C_Stop();

}

void main()
{
          int i;
          char mybyte;
          char myarray[8];
          char myarray2[8];
          char rdarray[16];
         
          for(i=0;i<8;i++)
          {
                myarray[i]=i;
                myarray2[i]=i+0x08;    

          }

          Write_One_Byte(0x20,0x28);

          Write_A_Page(myarray,0x10);
          Write_A_Page(myarray2,0x18);

          mybyte=Read_One_Byte(0x20);
          Read_N_Bytes(rdarray,16,0x10);

}

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