Y0       Y0 = long space disconnect disable.  When you send a
          break (a long space -- a long string of binary zeroes),
          it should be interpreted simply as a "Wait, stop, hold
          everything, just a minute there!" NOT as a hang up
          request.
          Y1 = when you have a modem so brain damaged you cannot
          get it to hang up, you might consider using Break as a
          way of getting it to hang up.  With Y1 the break is
          interpreted as "hang up".