.ORG $4000
    BLDSP $EFFF
    BLDX $F000
    SETIM
    BLDIV INT

BE: LDA [0,X]
    STA [$F020]
    JMP [BE]


INT:    CLRIM
    LDA [N]
    CMPA $00
    JZ [PLUS]
    LDA [N]
    DECA
    STA [N]
    DECX
    RTI


PLUS:   LDA [N]
    INCA
    STA [N]
    INCX
    RTI

    JMP [$0000]

N:  .BYTE $00
    .END