.ORG    0H

MAIN    MOV     A,R7
        OUTL    P1,A
        MOV     A,R6
        OUTL    P2,A
        CLR     A
        INC     A
        OUTL    BUS,A
        CLR     A
        OUTL    BUS,A
        JNT1    GETCODE
        JMP     MAIN

GETCODE CLR     A
        MOV     T,A
        JNT1    $
        STRT    T
        JTF     TIMEOUT
        JT1     $-2
        STOP    TCNT
        MOV     A,T
        CLR     C
        RRC     A
        CLR     C
        RRC     A
        CLR     C        
        RRC     A
        MOV     R0,A
        CLR     C
        RRC     A
        ADD     A,R0
        CPL     A
        INC     A
        MOV     R3,A
        CLR     F0
        CALL    GETBYTE
        JF0     MAIN
        CLR     F0
        CALL    GETBYTE
        JF0     MAIN
        CLR     F0
        CALL    GETBYTE
        JF0     MAIN
        MOV     R7,A
        CLR     F0
        CALL    GETBYTE
        JF0     MAIN
        MOV     R6,A
        CALL    LONGDLY
        JMP     MAIN


GETBYTE CLR     A
        MOV     R5,#08H
GETBIT  CLR     C
        RLC     A
        MOV     R2,A
        CLR     A
        MOV     T,A
        JNT1    $
        STRT    T
        JTF     TIMEOUT
        JT1     $-2
        STOP    TCNT
        MOV     A,T
        CLR     C
        ADD     A,R3
        JNC     ZERO
        INC     R2
ZERO    MOV     A,R2
        DJNZ    R5,GETBIT
        RET

TIMEOUT CPL     F0
        RET
        
DELAY   MOV     R0,#0FFH
DEB1    DJNZ    R0,DEB1
        RET
        
LONGDLY MOV     R1,#0FFH
D2      CALL    DELAY
        DJNZ    R1,D2
        RET


.END