CODE _blank ( this is way too slow in Forth )
    A XORr, VDP_CTLPORT OUTnA,
    A 0x40 LDrn, VDP_CTLPORT OUTnA,
    HL 0x4000 LDddnn,
    BEGIN,
        A XORr, VDP_DATAPORT OUTnA,
        HL DECss, HLZ,
    JRNZ, AGAIN,
;CODE

