Save Data Pointer (02); Restore Pointers (03); Disconnect (04); Initiator Detected Error (05) - IBM Ultrastar 36LZX Specifications

DT_REQ A bit of zero for DT_REQ (Double Transition Enable Request) indicates that DT DATA phases
are to be disabled when received from the originating SCSI device and that DT DATA phases are not
supported when received from the responding SCSI device.
A DT_REQ bit of one indicates that DT DATA phases are to be enabled when received from the
originating SCSI device and that DT DATA phases are supported when received from the responding
SCSI device.
IU_REQ (Information Unit Request) is not supported. The bit should be 0.

10.1.5 SAVE DATA POINTER (02)

This message is sent from the drive to direct the initiator to copy the active data pointer to the saved
data pointer. The SAVE DATA POINTER message is only sent if the initiator has previously indicated the
ability to accommodate disconnection and reconnection via the IDENTIFY message.
The drive will send the SAVE DATA POINTER message to the initiator prior to sending a DISCONNECT
message to the initiator if a data phase has occurred and another data phase is required to successfully
complete the command.

10.1.6 RESTORE POINTERS (03)

This message is sent from the drive to direct an initiator to copy the most recently saved pointers to the
corresponding command, data, and status pointers. Command and status pointers should be restored
to the beginning of the present command and status areas. The data pointer should be restored to the
value at the beginning of the data area in the absence of a SAVE DATA POINTER message or to the
value at the point at which the last SAVE DATA POINTER message occurred. Also see SCSI Bus
Related Error Handling Protocol on page 207.

10.1.7 DISCONNECT (04)

This message is sent from the drive to inform an initiator that the present connection is going to be
broken. A later reconnect will be required in order to complete the current command. The disconnection
serves to free the SCSI bus while the drive performs a relatively long operation that does not require the
bus. These messages are sent only if the initiator previously indicated (via the IDENTIFY message) the
ability to accommodate disconnection and reconnection.
The DISCONNECT message may also be sent from the initiator to the drive to disconnect from the SCSI
bus. The drive does not support the DISCONNECT message from the initiator. And it always responds
by sending MESSAGE REJECT message to the initiator.

10.1.8 INITIATOR DETECTED ERROR (05)

This message is sent from an initiator to inform the drive that an error has been detected that does not
preclude the drive from retrying the previous COMMAND, DATA and STATUS phase. The source of the
error may be either related to previous activities on the SCSI bus or may be internal to the initiator and
unrelated to any previous SCSI bus activity
If the initiator intends to send this message, the initiator must assert the ATN signal prior to its release of
ACK for the last byte transferred in the information phase that is to be retried. This provides an interlock
so the drive can determine which information phase to retry.
After receiving this message the drive may retry the previous phase by sending a RESTORE POINTERS
message to the initiator and then repeating the previous COMMAND, DATA, or STATUS phase.
Ultrastar 36LZX hard disk drive specifications
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