The Serial Port interface for platform drives operates in the following four modes:

(0) Power-savings Mode

   Power-on default (only if drive supports Power-savings at power on, aka "APM ASAP").

   This mode can be disabled ONLY by entering an ESCAPE character ("ESC").

   This mode is enabled automatically by the drive itself.

   In this mode, the drive will NOT respond to either ESLIP encoded packets or ASCII
   characters over the serial port interface.  In this mode, the native interface (SATA,
   SCSI, SAS, FC) will respond only to those commands that are allowed when the drive is
   in power-savings modes.

(1) ESLIP Mode

   Power-on default (unless drive supports Power-savings at power on, aka "APM ASAP").

   This mode is enabled by Control-T.

   In this mode, the drive will respond only to ESLIP encoded packets received over the
   serial port interface.  The ASCII diagnostic commands described in this document are
   not available in this mode.  In this mode, the native interface (SATA, SCSI, SAS, FC)
   is alive.  This is the default power on mode for the serial port interface unless drive
   supports Power-savings at power on (aka "APM ASAP").

      - Entering a Control-T character from YASPP (or any similar host serial port
        program) while the drive serial port is in ASCII Online mode or ASCII
        Diagnostic mode will switch the serial port to ESLIP mode.

      - Entering a Control-R character while the drive serial port is in ESLIP mode
        will switch the serial port to ASCII Online mode.

      - Entering a Control-Z character while the drive serial port is in ESLIP mode
        will switch the serial port to ASCII Diagnostic mode.

(2) ASCII Online Mode

   This mode is enabled by Control-R.

   In this mode, the drive will respond only to the ASCII Online commands described in
   this document.  It will not respond to ESLIP encoded packets received over the serial
   port interface.  In this mode, the native interface (SATA, SCSI, SAS, FC) is alive.

      - Entering a Control-R character from YASPP (or any similar host serial port
        program) while the drive serial port is in ESLIP mode or ASCII Diagnostic
        mode will switch the serial port to ASCII Online mode.

      - Entering a Control-Z character while the drive serial port is in ASCII Online
        mode will switch the serial port to ASCII Diagnostic mode.

      - Entering a Control-T character while the drive serial port is in ASCII Online
        mode will switch the serial port to ESLIP mode.

      - Entering a : character while the drive serial port is in ASCII Online mode will
        switch the serial port to Secondary Online Mode.

(3) ASCII Secondary Online Mode

   This mode is enabled by :

   In this mode, the drive will respond only to the ASCII Secondary Online commands described
   in this document.  It will not respond to ESLIP encoded packets received over the serial
   port interface.  In this mode, the native interface (SATA, SCSI, SAS, FC) can be alive.

      - Entering any character will execute the corresponding command (if any).  Whether a
        command was executed or not, the drive will exit Secondary Online Mode, returning
        to whatever state the drive was in before entering Secondary Online Mode.

(4) ASCII Diagnostic Mode

   This mode is enabled by Control-Z.

   In this mode, the drive will respond to all ASCII commands described in this document.
   It will not respond to ESLIP encoded packets received over the serial port interface.
   In this mode, the native interface (SATA, SCSI, SAS, FC) is not alive.

      - Entering a Control-Z character from YASPP (or any similar host serial port
        program) while the drive serial port is in ESLIP mode or ASCII Online mode will
        switch the serial port to ASCII Diagnostic mode.

      - Entering a Control-R character while the drive serial port is in ASCII Diagnostic
        mode will switch the serial port to ASCII Online mode.

      - Entering a Control-T character while the drive serial port is in ASCII Diagnostic
        mode will switch the serial port to ESLIP mode.