SCON1   EQU     0C0H
RI1     EQU     SCON1.0
TI1     EQU     SCON1.1
RB81    EQU     SCON1.2
TB81    EQU     SCON1.3
REN1    EQU     SCON1.4
SM21    EQU     SCON1.5
SM11    EQU     SCON1.6
SM01    EQU     SCON1.7

ES1     EQU     IE.6

SBUF1   EQU     0C1H
WDCON   EQU     0D8H

        ORG     0000H
        LJMP    START
        ORG     0003H
        LJMP    INT_0
        ORG     0023H
        LJMP    SIO_0
        ORG     003BH
        LJMP    SIO_1
        ORG     005BH
        LJMP    INT_2

START:
        MOV     IE,#0       ;DISABLE ALL INTERRUPT
        MOV     TMOD,#020H  ;TIMER1:MODE 2 (8BIT RELOAD)
        MOV     TH1,#0F3H   ;2400BPS @ 12MHz
        MOV     TL1,#0F3H
        ANL     PCON,#07FH  ;CLEAR SMOD BIT FOR SIO0
        ANL     WDCON,#07FH ;CLEAR SMOD BIT FOR SIO1
        CLR     ET1

        MOV     SCON,#50H   ;
        MOV     SCON1,#50H
        SETB    TR1

        SETB    ES
        SETB    ES1
        SETB    IT0
        SETB    EX0
        SETB    0EBH    ;ENABLE EXT2 INTERRUPT

        SETB    EA
        NOP
        MOV     A,#055H
        MOV     SBUF,A
        MOV     A,#0AAH
        MOV     SBUF1,A

        NOP
        SJMP    $

INT_2:
        ANL     91H,#7FH   ;CLEAR INTERRUPT FLAG
        NOP
        NOP
        RETI

INT_0:
        NOP
        NOP
        RETI

SIO_0:
        CLR     ES
        JNB     TI,S0_R
        CLR     TI
        NOP
        SJMP    S0_RET
S0_R:
        CLR     RI
        MOV     A,SBUF
        NOP
S0_RET:
        SETB    ES
        RETI

SIO_1:
        CLR     ES1
        JNB     TI1,S1_R
        CLR     TI1
        NOP
        SJMP    S1_RET
S1_R:
        CLR     RI1
        MOV     A,SBUF1
        NOP
S1_RET:
        SETB    ES1
        RETI

        END