\ To use this, poke $FC with the character to fill the screen with, then
\ SYS or JSR the appropriate address to invoke this function.

:= FillScreen

    0 #b, ldx,
    $fc dp, lda,

    begin,
        $0400 $,x, sta,
        $0400 250 + $,x, sta,
        $0400 500 + $,x, sta,
        $0400 750 + $,x, sta,
        inx, 250 #b, cpx,
    untileq,
    rts,