$NOMOD51

$NOLIST
    #include <reg517.h>
$LIST

LJMP    START
ORG 100H

START:
    MOV R4, #0
    MOV R2, #0x77
    ANL P5, #0x0F
    ORL P5, #0xF0
INPUT:
    MOV A, R2
    RR  A
    MOV R2, A

    MOV B, A
    JB  B.0, INPUT2
    XCH A, R4
    JNZ INPUT3
    MOV P1, #0xFF
INPUT3:
    XCH A, R4
    MOV R4, #0
INPUT2:
    ORL A, #0x0F
    ANL P5, #0x0F
    ORL P5, #0xF0
    ANL P5, A
    MOV     R3, A

    MOV A, P7
    ORL A, #0xF0
    MOV R0, A
    XRL A, #0xFF
    JZ  INPUT

    INC R4
    MOV A, R0
    ANL A, R3
    MOV P1, A
    JMP INPUT

    NOP
    NOP
    NOP
    JMP $
END START