Sleep:
   ld a, 2
   out (10h), a ; Disable LCD
   di ; And interrupts, for now
   im 1 ; interrupt mode 1, for cleanliness
   ei ; Enable interrupting when ON is pressed
   ld a, 1h
   out (03h), a ; ON
   halt ; and halt :)
   ld a, 0Bh ; Reset the interrupts
   out (03h), a
   ld a, 3
   out (10h), a ; Enable the screen
   ret