hello.z80

org 64000
     ld hl, 22625       ; load a memory address (screen attribute)
     ld a, 17           ; repeating time for 17 vertical rows
loop ld b,30            ; repeating time for 30 blocks row
row  ld (hl),69         ; load attribute value (into address)
     inc hl             ; increment address
     djnz row           ; decrement jump if not zero (till 'b' reaches 0)
     inc hl
     inc hl             ; jump next row, col 1
     dec a              ; decrement column counter
     jr nz, loop        ; jump till all registers are not zero
     ret