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CDU-541 CD-ROM DRIVE SCSI INTERFACE MANUAL
Only one logical unit number shall be identified for anyone selection
sequence;
a second IDENTIFY message with a new logical unit number shall not
be issued before the bus has been released (BUS FREE phase).
The initiator
may send one or more IDENTIFY messages during a selection sequence.
However,
'~
the logical unit number in any additional IDENTIFY messages shall be the same
as the logical unit number specified in the first IDENTIFY message sent by the
initiator.
When sent from the controller to an initiator during reconnection, an
implied RESTORE POINTERS message shall be performed by the initiator prior to
completion of this message.
4.5.
Handling of Status Phase
The controller will always follow the selection phase with a command phase.
If exception handling requires a status phase it will occur after the command
phase.
(Example:
A reservation conflict or busy status.)
A status byte will be sent from the controller to the initiator during the
STATUS phase at the termination of each command unless the command is cleared
by an ABORT message, by a BUS DEVICE RESET message, an assertion of the RST
signal, or by an unexpected BUS FREE condition.
4.5.1.
Status Byte Description
GOOD (OOh).
This status indicates that the controller has successfully
completed the command.
CHECK CONDITION (02h).
This status indicates that an error, exception, or
abnormal condition has caused the sense key or additional sense code to
be
set. The REQUEST SENSE command should be issued following a CHECK CONDITION
status, to determine the nature of the condition.
BUSY (oBh).
This status indicates that the controller is busy.
The
controller is unable to perform a command from an otherwise acceptable
initiator.
The normal initiator recovery action is to issue the command again
at a later time.
INTERMEDIATE (lOh).
This status indicates that a command in a series of
linked commands has completed successfully.
This status is returned for every
linked command in a series of linked commands except the last command, unless
an error, exception, or abnormal condition causes a CHECK CONDITION status·or
a RESERVATION CONFLICT status to be returned.
If the intermediate status is
not returned, the chain of linked commands is broken; no further commands in
the series are executed.
RESERVATION CONFLICT
(18h)~
This status indicates that the initiator
attempted to access a logical unit that is reserved for to another SCSI ID.
The normal initiator recovery action is to issue the command again at a later
time.
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