Purpose Make a loop that will fill the first eight rows of the Video Memory with %11111111.
Code
	ld hl,$fc00		;address of start
				; of video memory
	ld b,$10*8		;do 8 rows (16
				; bytes in each row)
loop:
	ld (hl),%11111111	;what to put at
				; that address
	djnz loop		;repeat until b=$00
	
Error We keep filling the same byte (the byte at $fc00) over and over again with %11111111. We need to increase hl (inc hl) so it points to the next byte after each successive loop.

Speed up the routine by preloading a with the value to fill (hl) with before we start the loop.

Fixed Code
	ld hl,$fc00		;start address of
				; video memory
	ld b,$10*8		;do 8 rows (16 bytes
				; per row)
	ld a,%11111111		;what to put at that
				; address
loop:
	ld (hl),a		;load up that address
	inc hl			;increase to next address
	djnz loop		;repeat until b=$00