HP C737990900 - Manual (Page 32)

32 Commands—Introduction
Command Details
The command descriptions in this section are listed in alphabetical order of
command name. Each command is described briefly. This is followed by a list
of pre-execution checks which are described below. The Command Descriptor
Block (CDB) is then given, with details of the various parameter bits and fields.
Pre-Execution Checks
Note In compliance with the SCSI specification, the drive terminates a
command with a CHECK CONDITION status and sets the sense
key to ILLEGAL REQUEST when a reserved bit, byte, field or code
is received which is not zero.
Before executing a command, the drive makes a number of checks. They fall
into three categories:
■
Checks on the command sent by the host. These ensure that no reserved or
fixed fields have been set to illegal values. They check the syntax of
commands, in other words the cross dependency of fields. For example, the
Flag bit must not be set if the Link bit is not set.
■
Checks to ensure that there are no outstanding UNIT ATTENTION or
DEFERRED ERROR events posted for the host that has sent the command.
■
Checks on media access abilities. These are performed for commands
requiring access to the cartridge. A command is rejected if it attempts to
access the cartridge when no cartridge is present or the cartridge is
unloaded.
The checks are described below in alphabetical order. The usual order of
execution is Illegal Field, Fixed Bit, Flag Link, Bad LUN, Reservation, Deferred
Error, Unit Attention, Media Access, Media Write, Diagnostic Status, Humidity,
Parameter List.
Bad LUN Check
For all commands except INQUIRY 12h, this checks that the LUN specified by
the host is zero. The LUN is taken from the lowest 5 bits of the host’s IDENTIFY
message.