i am in try to receive a byte from pc on microcontroller at89c51, but SBUF always have a value "0" whatever i send from pc. i am using following code. please let me know what is wrong with this code.
#include <at89x51.h>
unsigned char freqq;
void serial(void) ;
void main()
{
P0=0xff;
P2=0xff;
P3=0xff;
P1=0xff;
EA = 1;
ES=1;
TMOD |= 0x20;
TH1=0xf3;
TR1 = 1;
SCON = 0x52;
while(1)
{ ; }
}

void serial(void) interrupt 4
{

if(RI)
{
RI=0;
P0=SBUF;
}
}