UART receive ADUC836

Hi everybody!!!

I'm new and i need some help!!!

Nice to meet you!!!

I'm trying to connect my Aduc836 (8051 architecture) with a 4d systems display by Serial TTL.

What i want to do for this moment it's simply send a char by the display and turn on one led on my boards....
the problem I have is that I can not read properly the character sending by the display.

Below the code on my MCU:

#include <reg52.h>

sbit P3_4 = P3^4;
sbit P3_5 = P3^5;

bit flag = 0;

idata unsigned char rx;

void UART_intialization(void)
{
SCON = 0x50;   // 8 bit, variable baud rate + REN = 1;

TMOD &= ~0xF0;    // timer1 bit set to 0
TMOD |= 0x20;      // timer 1, autoreload

TL1 = 252;      // baud rate 9600
TH1 = 252;

ES = 1;     // interrupt serial enable
EA = 1;     // all interrupt souce enabled;
TR1 = 1;     // start timer1
}


void int_Serial(void) interrupt 4
{
if(RI != 0 )
{
RI = 0;
rx = SBUF;
flag = 1;
}
}

void main(void)
{
UART_initialization();


while(1)
{
if( flag )
{
if( rx == 'a' ) P3_4 = 0;   // if i read the correct value ( i send by display the char 'a')
                             // i turn on one led
else P3_5 = 0;              // else if the value that i read it's wrong i turn on another led
}
flag = 0;
}
}

the code send by the display it's a simple instruction serout('a') , that works correctly.

Any advice?