ld hl, $C011    ; CRAM address $0011 with top two bits set to indicate a CRAM write
    ld c, $BF       ; writing to control port
    out (c), l      ; output address 
    out (c), h      ; 

    ld a, $3F       ; for the SMS, setting all six colour bits makes white
    out ($BE), a    ; data port write