Save Data Po I Nt E R (02); Restore Pointers (03); Disconnect (04) - IBM DDRS-39130 - Ultrastar 9.1 GB Hard Drive Specifications

Note: If the corresponding transfer width exponent received from the Initiator indicates a data transfer width
that is greater than 16 bits (E > 01h) the Target sends a Message Reject message to the initiator to indicate
8 bit data transfer mode.
If the first message received from the Initiator is either a Message Parity Error or a Message Reject message,
the Target goes to 8 bit data transfer mode. For the Message Parity Error case, the wide data transfer nego-
tiation is restarted if the Target successfully retransmits the Wide Data Transfer Request message to the Initi-
ator.
If the first message received from the Initiator is any other message, the Target goes to 8 bit data transfer
mode. The Target assumes that the Initiator does not support wide data transfer and does not attempt to
renegotiate with this Initiator.
The implied agreement for wide data transfer operation is not considered to exist by the Target until the
Target leaves the Message Out phase, implying that no parity error was detected. If the Target detects a
parity error while attempting to receive the message from the Initiator, the Target goes to 8 bit data transfer
mode. The Target will attempt to resume the wide data transfer negotiation by retrying the Message Out
phase.
Note: If during the Message In phase of negotiations, either Target or Initiator started, ATN is asserted
prior to transmission of the last byte of the message and the message is not Message Parity or Message
Reject, the Target goes to 8 bit data transfer mode.
9.1.4 SAVE DATA POINTER (02)
This message is sent from the file to direct the initiator to copy the active data pointer to the saved data
pointer. The SAVE DATA PO I NT E R message is only sent if the initiator has previously indicated the
ability to accommodate disconnection and reconnection via the IDENTIFY message .
The file will send the SAVE DATA P OI N TE R 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 com-
plete the command.

9.1.5 RESTORE POINTERS (03)

This message is sent from the file to direct an initiator to copy the most recently saved pointers to the corre-
sponding 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 PO I N T ER message or to the value at the point
at which the last SAVE DATA PO I NT ER message occurred. Also see 9.4, "SCSI Bus Related Error Han-
dling Protocol" on page 175.

9.1.6 DISCONNECT (04)

This message is sent from the file 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 is to free
the SCSI bus while the file performs a relatively long operation that does not require the bus. These mes-
sages are only sent if the initiator previously indicated (via the IDENTIFY message) the ability to accommo-
date disconnection and reconnection.
The DISCONNECT message may also be sent from the initiator to the file to disconnect from the SCSI
bus. The file does not support the DISCONNECT message from the initiator. And it always respond by
sending MESSAGE REJECT message to the initiator.
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SCSI MESSAGE SYSTEM