#include <reg51.h>
sbit BT_SND    =P1^0;
sbit BT_REC    =P1^1;
/**********************************************
    
    IO 口模擬232通訊程序
    
    使用兩種方式的C程序 占用定時器0 
    
**********************************************/

#define MODE_QUICK

#define F_TM F0

#define TIMER0_ENABLE     TL0=TH0; TR0=1;
#define TIMER0_DISABLE        TR0=0;

sbit ACC0=   ACC^0;
sbit ACC1=   ACC^1;
sbit ACC2=   ACC^2;
sbit ACC3=   ACC^3;
sbit ACC4=   ACC^4;
sbit ACC5=   ACC^5;
sbit ACC6=   ACC^6;
sbit ACC7=   ACC^7;

void IntTimer0() interrupt 1
{
    F_TM=1;
}
//發送一個字符
void PSendChar(unsigned char inch)
{
#ifdef MODE_QUICK    
    ACC=inch;

    F_TM=0;
    BT_SND=0;        //start bit 
    TIMER0_ENABLE;    //啟動
    while(!F_TM);
    
    BT_SND=ACC0;    //先送出低位
    F_TM=0;
    while(!F_TM);
    
    BT_SND=ACC1;    
    F_TM=0;
    while(!F_TM);
    
    BT_SND=ACC2;    
    F_TM=0;
    while(!F_TM);

    BT_SND=ACC3;    
    F_TM=0;
    while(!F_TM);

    BT_SND=ACC4;    
    F_TM=0;
    while(!F_TM);
    
    BT_SND=ACC5;    
    F_TM=0;
    while(!F_TM);

    BT_SND=ACC6;    
    F_TM=0;
    while(!F_TM);
    
    BT_SND=ACC7;    
    F_TM=0;
    while(!F_TM);

    BT_SND=1;    
    F_TM=0;
    while(!F_TM);
    
    
    TIMER0_DISABLE;    //停止timer
#else
    unsigned char ii;
    
    ii=0;
    
    F_TM=0;
    BT_SND=0;        //start bit 
    TIMER0_ENABLE;    //啟動
    while(!F_TM);
    
    while(ii<8)
    {
        if(inch&1)
        {
            BT_SND=1;
        }
        else
        {
            BT_SND=0;
        }
        F_TM=0;
        while(!F_TM);
        ii++;
        inch>>=1;
    }
        BT_SND=1;    
        F_TM=0;
        while(!F_TM);

#endif    
    TIMER0_DISABLE;    //停止timer
}
//接收一個字符
unsigned char PGetChar()
{
#ifdef MODE_QUICK    

    TIMER0_ENABLE;    
    F_TM=0;
    while(!F_TM);    //等過起始位
    ACC0=BT_REC;
    
    TL0=TH0;

    F_TM=0;
    while(!F_TM);
    ACC1=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC2=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC3=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC4=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC5=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC6=BT_REC;
    
    F_TM=0;
    while(!F_TM);
    ACC7=BT_REC;
    
    F_TM=0;
    
    while(!F_TM)
    {
        if(BT_REC)
        {
            break;
        }        
    }
    TIMER0_DISABLE;    //停止timer
    return ACC;
#else
    unsigned char rch,ii;
    TIMER0_ENABLE;    
    F_TM=0;
    ii=0;
    rch=0;
    while(!F_TM);    //等過起始位
    
    while(ii<8)
    {
        rch>>=1;
        if(BT_REC)
        {
            rch|=0x80;
        }
        ii++;
        F_TM=0;
        while(!F_TM);
                
    }
    F_TM=0;
    while(!F_TM)
    {
        if(BT_REC)
        {
            break;
        }
        
    }
    TIMER0_DISABLE;    //停止timer
    return rch;
    
#endif    
    
}
//檢查是不是有起始位
bit StartBitOn()
{
    return  (BT_REC==0);
    
}
void main()
{
    unsigned char gch;
    
    TMOD=0x22;        /*定時器1為工作模式2(8位自動重裝)，0為模式2(8位
自動重裝) */
    PCON=00;

    TR0=0;            //在發送或接收才開始使用
    TF0=0;        
    TH0=(256-96);    //9600bps 就是 1000000/9600=104.167微秒 執行的
timer是
                    //             
104.167*11.0592/12= 96 
    TL0=TH0;
    ET0=1;
    EA=1;
    
    PSendChar(0x55);
    PSendChar(0xaa);
    PSendChar(0x00);
    PSendChar(0xff);

    while(1)
    {
        if(StartBitOn())
        {
            gch=PGetChar();
            PSendChar(gch);
        }
    }