ERDEV returns an error code from the last device that generated a critical
error. ERDEV$ returns the name of the device that generated the error.
 
ERDEV
ERDEV$
 
    - The low byte of the value returned by ERDEV contains the DOS error
      code. The high byte contains device-attribute information.
 
<EXAMPLE>
 
See Also    <ERR, ERL>    <ON ERROR>