SCSI Interface Overview
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5
When spacing, locating, or generally performing any tape motion when data cannot
be transferred on the SCSI bus.
During the time the Target is disconnected for one of these functions, the bus is free
for use by other devices. The Target initiates both disconnect and reconnect.
If the tape drive is selected while disconnected, it only allows the following actions:
If the command is from a different initiator or is from the same initiator but to a
different LUN, the tape drive accepts the command. If the command is a media-
access command the tape drive disconnects immediately. If the new command is a
REQUEST SENSE, INQUIRY or TEST UNIT READY, then the new command is
executed immediately.
Immediately following selection, the Initiator may send the Identify, No Op, Abort, or
Bus Device Reset messages to the drive.
If the command is from the same initiator to the same LUN, the current command
terminates with a Check Condition and an Abort Sense Key.
2.3.3
SCSI Messages
The SCSI message codes, descriptions, and directions are given in the following
table. Each of these SCSI messages are supported by the Quantum LTO drive.
Code Description
Direction
00h Command
Complete
In
01h Extended
Message*
In/Out
02h
Save Data Pointer
In
03h Restore
Pointers
In
04h Disconnect
In
05h
Initiator Detected Error
Out
06h Abort
Out
07h Message
Reject
In/Out
08h No
Operation
Out
09h Message
Parity
Error
Out
0Ch
Bus Device Reset
Out
23h
Ignore Wide Residue
In
80h+ Identify
In/Out
Notes: In = Drive to host; Out = Host to drive
* Only three extended messages are supported: Parallel Protocol Request, Synchronous Data Transfer
Request and Wide Data Transfer Request.
2.3.4
Inbound messages
The following table lists drive to host SCSI messages and their definitions.
Message Hex
Code
Definition
Command
Complete
00h
This message is sent by the drive at the end of the status phase to
indicate that a command is complete. Once the message is sent, the
drive releases the bus and goes to Bus Free
Disconnect 04h
This message is sent by the drive to indicate that it is about to
disconnect from the bus and go to Bus Free. During a Data phase, it
is always preceded by a Save Data Pointers message. If a Message
Reject message is received in response to this message, then the
drive will not disconnect.
Summary of Contents for LTO 4
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