在PC上用并行口模拟I2C总线的C源代码实例

在微机上模拟I2C总线的设计中，用并行口的D0（PIN2）模拟SCL信号，用D1（PIN3）模拟SDA信号。根据IIC总线的电平规范，程序如下：
    #include <dos.h>
    #include <stdio.h>
    #include <conio.h>
    #include <bios.h>

    #define DELAY_TIME 10
    #define FALSE 0
    #define TRUE 1
    const unsigned char SCL_PIN=0x01;
    const unsigned char SDA_OIN=0x02;

    static void SET_SCL(void)
    {
        asm{
            mov dx,0x378
            in  ax,dx
            or  ax,SCL_PIN            //将SCL置1
            out dx,ax
        }
    }

    static void CLR_SCL(void)
    {
        asm{
            mov dx,0x378
            in  ax,dx
            or  ax,0xff-SCL_PIN       //将SCL置0
            out dx,ax
        }
    }

    static void SET_SDA(void)
    {
        asm{
            mov dx,0x378
            in  ax,dx
            or  ax,SDA_PIN            //将SDA置1
            out dx,ax
        }
    }

    static void CLR_SDA(void)
    {
        asm{
            mov dx,0x378
            in  ax,dx
            or  ax,0xff-SDA_PIN       //将SDA置0
            out dx,ax
        }
    }

    void DELAY(int t=DELAY_TIME)      //延时子程序
    {
        for(int i=0;i<t;i++);
    }

    void IIC_Start(void)              //启动I2C总线
    {
        //在SCL为高电平时，使SDA出现一个负跳变
        SET_SDA();
        SET_SCL();
        DELAY();
        CLR_SDA();
        DELAY();
        CLR_SCL();
        DELAY();
    }

    void IIC_Stop(void)               //终止I2C总线
    {
        //在SCL为高电平时，使SDA出现一个正跳变
        CLR_SDA();
        SET_SCL();
        DELAY();
        SET_SDA();
        DELAY();
        CLR_SCL();
        DELAY();
    }

    void SEND_0(void)                //发送BIT0
    {
        //在SCL为高电平时，使SDA保持低电平
        CLR_SDA();
        SET_SCL();
        DELAY();
        CLR_SCL();
        DELAY();
    }

    void SEND_1(void)                //发送BIT1
    {
        //在SCL为高电平时，使SDA保持高电平
        SET_SDA();
        SET_SCL();
        DELAY();
        CLR_SCL();
        DELAY();
    }

    int Check_Acknowledge(void)
    {
        //发送完每个字节检查SLAVE的应答信号
        SET_SDA();                   //主器件释放SDA线
        SET_SCL();
        DELAY(DELAY_TIME/2);
        unsigned char b=inportb(0x378);    //采样信号线
        DELAY(DELAY_TIME/2);
        CLR_SCL();
        DELAY();
        if(b&0xSDA_PIN)            //SALVE返回1
            return FLASE;
        return TRUE;
    }