8 read only, mit 7 and 0 are checked
18h
0bh ????
0ch Command/Status Reg
  out
    08h     Restore h=1 -> Load head at beginning
    78h     Step out, u=1 -> Update track register
    80h     read sector
    d0h     force interrupt
0dh Track Reg ?
0eh Sector Reg ?

14h Drive Select ??
