User's Manual

DLT4000 SCSI Interface
DLT4000/DLT4500/DLT4700 Cartridge Tape Subsystem 8-25
8.4.5 LOAD-UNLOAD (1Bh)
Bit
7 6 5 4 3 2 1 0
0 Operation Code (1Bh)
1 Logical Unit Number Reserved Long
Byte 2 Reserved
3 Reserved
4 Reserved EOT Re-Ten Load
5 Unused Reserved Flag Link
Figure 8-10 LOAD-UNLOAD CDB
LOAD-UNLOAD tells the target to load or unload the media in the tape cartridge. If
no cartridge is in the drive, both LOAD and UNLOAD will return a CHECK
CONDITION status with a NOT READY sense key set. If the drive has received an
UNLOAD command with the Immed bit set and then receives another command
which would involve tape motion or TEST UNIT READY, the drive will return a
CHECK CONDITION status with a NOT READY sense key set.
Operation of the Unload version of this command will be different if a media loader is
present.
Two modes of operation are possible when a media loader is attached. If none of the
media loader specific commands has been issued, then the device will operate in the
sequential mode of operation. Once a media loader specific command has been issued,
the sequential mode of operation is disabled and the UNLOAD command becomes a
no-op.
If the device is still in the default sequential mode of operation and an UNLOAD
command is received by the subsystem, the current cartridge will be unloaded and
automatically moved to the magazine slot from which it originated. Then, the
cartridge from the next slot in the magazine, if not empty, is automatically moved
from the magazine into the drive, loaded, and made ready. If the next magazine slot is
empty, no CHECK CONDITION status is created.
When the cartridge is unloaded into magazine slot 6 (the last one), the subsystem does
not cycle back to slot 0. This prevents accidental overwriting of data when using the
subsystem in sequential auto-loading mode. The next cartridge must be selected and
loaded manually, or with a SCSI Move Medium command.
EEROM parameters ENALDRAUTOLD and DISLDRAUTOLDMC can be modified
to enable/disable the sequential loading feature (Table 8-4).
A media loader does not affect the device's processing of the LOAD flavor of the
LOAD-UNLOAD command.