When entered from DCL level, Ctrl/Y interrupts an image that is
    running without debugger control, enabling you then to start the
    debugger with the DCL command DEBUG.

                                  NOTES

       Do not use Ctrl/Y from within a debugging session. Instead,
       use Ctrl/C or an equivalent abort-key sequence established
       with the SET ABORT_KEY command.

       When you start the debugger with the Ctrl/Y-DEBUG sequence,
       you cannot then use the debugger RUN or RERUN commands.

    Format

      <Ctrl/Y>