User's Guide

Commands: Load/Unload (1Bh) Page 45
LOAD/UNLOAD (1Bh)
The LOAD/UNLOAD command requests that the DAT drive enable or disable the
logical unit for further operations.
When a LOAD command is executed, the tape is positioned to LBOT and made
ready for the next command.
When an UNLOAD command is executed, the tape positions to BOT, and the
cartridge is ejected without an error condition. The UNLOAD command ejects the
cartridge even if a PREVENT MEDIA REMOVAL command is in effect.
For the Autoloader, an UNLOAD command ejects the cartridge from the drive into
the storage element positioned in front of the drive and then inserts the next
cartridge in sequence.
LOAD/UNLOAD Command Descriptor Block
The following table shows the layout of the CDB.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 1 1 0 1 1
1 0 0 0 0 0 0 0 IMMED
2 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 RT LOAD
5 vendor unique* 0 0 0 0 Flag Link
* This vendor-unique field is reserved and must be set to zero.
Command Descriptor Block Field Description
The following table defines the fields in the CDB.
Field
Name Bytes Bits Description
IMMED
bit
1 0 If the IMMED bit is 1, status is returned as soon as the operation is
initiated. If the IMMED bit is 0, status is not returned until the tape is
positioned.
RT bit 4 1 Retension bit. No retension is necessary for DDS/DAT cartridges. For
software compatibility this field can be either 0 or 1.
LOAD
bit
4 0 If the LOAD bit is 1, the tape moves to BOT.
If the LOAD bit is 0, the tape repositions to BOT. The tape is then
ejected. Following an UNLOAD, the drive accepts and executes any
valid non-media access commands.