Oh, yes. How amazingly simple it is! Exactly I have read all the example code from all of you through, a little bit tiny and precise parts of them are better understanding with discussion here for me. Some applications get me cofused in that only a short time has passed since I started to handle with 8052.

Actually, my purpose for serial interrupt is to transmit 3 times in a cycle of ADC interrupt. ADC interrupt sounds to be called very well by each end of ADC in main. But then serial interrupt is still not well. No expected output coming, just nothing. Here is my code. Serial port mode 3 has been employed. Are there still some confusions or misunderstandings?

////////// UART SERIAL PORT INTERRUPT ROUTINE //////////
void serial(void) interrupt 4 {
if(TI) {
 TI = 0;
 SBUF = tmp;
 }
}

////////// ADC INTERRUPT ROUTINE //////////
void adc(void) interrupt 6 {
 if(!flag) {
  /* transmit data1 */
  tmp = data1;
  TB8 = 1;	// 9th bit = 1
  TI = 1;
  /**** NEED TRANSMISSION HERE! ****/
  flag = 1;
 }
 else if(flag) {
  /* transmit data2 */
  tmp = data2;
  TB8 = 0;	// 9th bit = 0
  TI = 1;
  /**** NEED TRANSMISSION HERE ****/
  /* transmit data3 */
  tmp = data3;
  TI = 1;
  /**** NEED TRANSMISSION HERE ****/
  flag = 0;
 }
}