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SCSI Messages and Status Codes
State or Phase
Data In Phase
Data Out Phase
Status Phase
Message In Phase
Message Out Phase
An Initiator that accommodates disconnect/reconnect can indicate this capability to
the tape drive during the Selection phase by asserting both its own Initiator SCSI ID
bit as well as the tape drive's SCSI ID bit (allows the tape drive to know with which
Initiator to reconnect). The Initiator must also assert ATN before exiting the Selection
phase (prior to releasing SEL) and send an Identify message out of C0h to the tape
drive. This sequence causes the drive to enter the Message-Out phase when the
Selection phase completes.
The first message sent by the host after the Selection phase is an Identify message.
Under normal conditions, the first message sent by the tape drive after a Reselection
phase is also Identify. Under certain exceptional conditions, the host may send the
Abort message or the Bus Device Reset message instead of Identify as the first
message.
Description
If the host detects a parity error while data is being transferred from the
drive and asserts ATN, the drive:
♦ Terminates the transfer of data.
♦ Switches the host to the Message Out Phase.
♦ Waits for the host to send a 05 (Host Detected Error).
♦ Switches the host to the Status Phase and sends a Check Condition.
♦ Switches the host to the Message In Phase and sends a Command
Complete.
♦ Sets the Sense Key = B and ASC/ASCQ = 48-00 (SCSI-2 only).
If the drive detects a parity error while the host is transferring data, the
drive:
♦ Terminates the transfer of data.
♦ Switches the host to the Status Phase and sends a Check Condition.
♦ Switches the host to the Message In Phase and sends Command
Complete.
♦ Sets the Sense Key = B and ASC/ASCQ = 47-00 (SCSI-2 only).
If the host is in the Status phase and detects an error in the status byte
and asserts ATN, the drive:
♦ Switches the host to the Message Out Phase and waits for the host to
send 05 (Initiator Detected Error).
♦ Switches the host to the Status Phase and sends a Check Condition.
♦ Target sends restore pointers and resends Status.
If the host is in the Message In Phase and detects an error on a message
bytes an asserts ATN, the drive:
♦ Switches the host to the Message Out Phase.
♦ Waits for the host to send 09 (Parity Error Message).
♦ Switches the host to the Message In Phase and resends the message.
♦ If the host is in the Message Out Phase and sends a message bytes
and the drive detects a parity error, the drive retries forever.
Page 13
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