Dear ALL, I have tried to program the serial port and simulated the serial port under the Keil. But it seems could work. All the related registers I have checked. The program just won't get into the uart_sub and loop in the main_loop. ;;Test Program ;;UART always send 0x41h out org 0000h ljmp start org 0023h ;serial communication int ljmp uart_sub org 0030h start: mov sp,#060h ;------UART Setting Start--------------------------------------------- mov tmod,#00100000b ;Timer0 Mode1,Timer1 Mode2 mov th1,#0fdh setb tr1 mov scon,#01010000b ;enable Receive mov ie,#10010000b ;enable UART Interrupt ;------UART Setting End----------------------------------------------- main_loop: ;;UART test start mov a,#041h mov sbuf,a jmp main_loop ;;UART test end ;;------------------------------------------ ;; ;; UART Subroutine Start ;; ;;------------------------------------------ uart_sub: push psw push acc jbc ri,rcv_data clr ti jmp uart_done rcv_data: COM port got data mov a,sbuf mov uart_buffer,a uart_done: pop acc pop psw reti ;;--------------------------------------------------------------------------------- ;; ;; UART Subroutine End ;; ;;--------------------------------------------------------------------------------- end