[求助] 用串口控制繼電器工作狀態(tài)

如下程序我想實現(xiàn)串口發(fā)不同的字符后，單片機(jī)P0口高電平驅(qū)動三極管工作。但是發(fā)現(xiàn)沒有辦法動作！求助！��！

#include <reg51.h> 
#include <string.h> 
#define INBUF_LEN 4 //數(shù)據(jù)長度 

unsigned char inbuf1[INBUF_LEN]; 
unsigned char checksum,count3;
bit read_flag= 0; 

sbit keypad1=P0^0;
sbit keypad2=P0^1;
sbit keypad3=P0^2;
sbit keypad4=P0^3;
sbit keypad5=P0^4;
sbit keypad6=P0^5;

void delay_ms(unsigned int ms)
{
unsigned int i;
unsigned char j;
    for(i=0;i<ms;i++)
    {
        for(j=0;j<200;j++);
        for(j=0;j<102;j++);
    } 
}

void init_serialcomm( void ) 
{ 
 SCON = 0x50 ; //SCON: serail mode 1, 8-bit UART, enable ucvr 
 TMOD |= 0x20 ; //TMOD: timer 1, mode 2, 8-bit reload 
 PCON |= 0x80 ; //SMOD=1; 
 TH1 = 0xF4 ; //Baud:4800 fosc=11.0592MHz 
 IE |= 0x90 ; //Enable Serial Interrupt 
 TR1 = 1 ; // timer 1 run 
 //TI=1; 
} 

//向串口發(fā)送一個字符 
void send_char_com(unsigned char ch) 
{ 
 SBUF=ch; 
 while (TI== 0 ); 
 TI= 0 ; 
} 

//向串口發(fā)送一個字符串，strlen為該字符串長度 
void send_string_com( unsigned char *str, unsigned int strlen) 
{ 
 unsigned int k= 0 ; 
 do 
 { 
  send_char_com(*(str + k)); 
  k++; 
 } 
 while (k < strlen); 
} 

//串口接收中斷函數(shù) 
void serial () interrupt 4 using 3 
{ 
 if (RI) 
 { 
  unsigned char ch; 
  RI = 0 ; 
  ch=SBUF; 
  if (ch> 127 ) 
  { 
   count3= 0 ; 
   inbuf1[count3]=ch; 
   checksum= ch- 128 ; 
  } 
  
  else 
  { 
   count3++; 
   inbuf1[count3]=ch; 
   checksum ^= ch; 
   if ( (count3==(INBUF_LEN- 1 )) && (!checksum) ) 
   { 
    read_flag= 1 ; //如果串口接收的數(shù)據(jù)達(dá)到INBUF_LEN個，且校驗沒錯，就置位取數(shù)標(biāo)志 
   } 
  } 
 } 
} 

void main(void) 
{ 
    unsigned char relay;
 relay='A';
 P0=0x00;
 init_serialcomm(); //初始化串口 
 while ( 1 ) 
 { 
  if (read_flag) //如果取數(shù)標(biāo)志已置位，就將讀到的數(shù)從串口發(fā)出 
  { 
      read_flag= 0 ; //取數(shù)標(biāo)志清0 
            //send_string_com(inbuf1,INBUF_LEN);
         send_char_com(relay);

   switch(relay) 
   {
       case 'B':
    delay_ms(500);
          keypad1=1;//氣缸1 Close
          delay_ms(2500);
             keypad2=1;//氣缸2 Close
    break;

    case 'C':
    delay_ms(500);
    keypad3=1;//氣缸3 Close
    delay_ms(1000);
    keypad3=0;//氣缸3 Open
    break;

    case 'D':
    delay_ms(500);
          keypad1=0;//氣缸1 Open
             keypad2=0;//氣缸1 Open
    break;

    case 'E':
             delay_ms(500);
          keypad4=1;//氣缸4 Close
          delay_ms(2500);
             keypad5=1;//氣缸5 Close
    break;

    case 'F':
               delay_ms(500);
     keypad6=1;//氣缸6 Close
    delay_ms(1000);
    keypad6=0;//氣缸6 Open
    break;

       case 'G':
                delay_ms(500);
             keypad4=0;//氣缸4 Open
             keypad5=0;//氣缸5 Open
    break;

    default:
    P0=0x00;
    break;
   }

  } 
 } 
}