;PROGRAM NAME S4.ASM
;TEST SERIAL PORT MODE 1 INPUT TEST
;
BUZZER  REG     P3.4
LED     REG     P3.7
;
RESET   MOV     R0,#00H
        DJNZ    R0,$
        CLR     LED
        CLR     BUZZER
;
        LCALL   INIT_SIO
START   CLR     RI
WAIT    JNB     RI,WAIT         ;WAIT UNTIL RI=1
        MOV     A,SBUF          ;READ A CHARACTER
        NOP
        NOP
        NOP
        NOP
        MOV     SBUF,A          ;OUTPUT TO SBUF
        CJNE    A,#'!',START
;
STOP    SJMP    STOP            ;ENDLESS LOOP
;
INIT_SIO
        MOV     TMOD,#00100000B ;TIMER 1 MODE 2
        MOV     TH1,#FDH        ;BAUD RATE=9600 BPS
        SETB    TR1             ;START TIMER 1
        MOV     SCON,#01010000B ;ENABLE RECEIVE
        RET                     ;1 START,8 BITDATA,1 STOP BIT