THank erik again!
I know that i should send data out when the TI was set.
any i have modify the code according to ur suggestion.
{if (TI)SBUF='a';}

if seems doesnt work.
I have no problem to send out the data by polling the TI bit.
How can i send a array[8] out byte by btye through serial interrupt method?

also, may i use the poll TI method to send data, and use the interrupt method to receive data? any draw back if i to do so.


#include <AT89X51.H>

void delay(int x);

void main ()
{
char ind=0;

TMOD=0x20;
TH1=-03;
TR1=1;
SCON=0x50;
IE=0x90;
P2_7=1;
delay(20000);

while(1)
{if (TI)SBUF='a';}

}

void RX() interrupt 4
{ char temp;
if (TI) //clear TI flag
{
TI=0;
}

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