sbit check=P3^7;                //making P3.7 a flag

void serial_init();
char serial_rec();

void serial_init()              // initializing the controller for 4800 baud
{RI=0;
TMOD=0x20;
TH1=0xFA;                       // 4800 baud rate
SCON=0x50;
TR1=1;
return;
}
char serial_rec()               //receiving data into SBUF by polling
{
while(RI==0);
RI=0;
return(SBUF);
}

void main()
{
unsigned char ch;
check=0;                        // making "check" flag zero
serial_init();                   
while(1)
{
ch=serial_rec();
if(ch==0x24)                    //HEX equivalent of ASCII'$' sign is 0x24
{check=1;                       //if '$' sign , make "check" HIGH
for(;;);                        // and infinite loop
 }
 else
 check=0;                       // else, "check" stays LOW.
}
}