cleartab:  .rept 1024  ; Table of 1024 zeroes
           .db   $00  
           .endr

           .rept 1024
           ldi
           .endr
ldiblk:    ret

 ld hl, cleartab       ; Quickly clear $c000-$c3ff
 ld de, $c000
 call ldiblk-1024*2