Quantum DLTtape DLT 4000, Product Manual

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SCSI Description
3-24 Quantum DLT 4000 Tape Drive
NOTES
In contrast to the BUSY status condition, the DRIVE NOT READY
Sense Key is returned as part of the Sense data following a REQUEST
SENSE command and indicates that a media access command has
been issued but that the media is not ready to be accessed. For
example, the tape cartridge is not installed, the tape medium has
been unloaded, the tape drive is currently initializing the tape
medium to prepare it for access, etc.
In the DRIVE NOT READY state, the initiator cannot perform any
operation that would cause tape motion (READ, WRITE, VERIFY, for
example). These commands return a CHECK CONDITION status with a
DRIVE NOT READY sense key. The initiator may execute commands
that do not require tape motion or access to the tape medium, and
a GOOD status may be the result.
3.6 SCSI BUS CONDITIONS
The SCSI bus has two asynchronous conditions: Attention and Reset.
3.6.1 Attention Condition
The attention condition informs a drive that an initiator has a message ready.
The drive gets the message by performing a MESSAGE OUT phase. The
attention condition requires the following timing:
•
The initiator creates the attention condition by asserting ATN at any time
except during the ARBITRATION or BUS FREE phases.
•
The initiator negates the ATN signal at least two deskew delays before
asserting the ACK signal while transferring the last byte of the message.
•
If the drive detects that the initiator failed to meet this requirement, then
the drive goes to BUS FREE.
•
Before transition to a new bus phase, the initiator asserts the ATN signal,
then waits at least two deskew delays before negating the ACK signal for
the last byte transferred in the current bus phase. Asserting the ATN signal
later cannot be honored until a later bus phase and then cannot result in
the expected action.
The drive responds with MESSAGE OUT as described in the following table: