Data overflow (ERR = 289)

  Either the keystroke retrieved  by  the  INKEY$  function  caused  the
  type-ahead  buffer  to  overflow  or, the terminal attempted to send a
  valid ANSI escape sequence that did not  correspond  to  a  keystroke.
  Specify the DCL command SET TERMINAL/HOSTSYNC, before using the INKEY$
  function.  This  command  will  prevent  the  type-ahead  buffer  from
  overflowing.