User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Overview of Command and Status Processing
Quantum DX-Series Software Interface Guide 111
Table 72 Command
Descriptor Block -
Field Descriptions
Note: Unless otherwise specified, all reserved bits indicated in the
commands are 0.
Field Description
Operation Code The operation code specifies the command being requested. The list of
supported SCSI commands and their operation codes are contained in
table 70
.
Logical Unit
Number
The Logical Unit Number contains the number of the device being
addressed. It must be set to 0. The Logical Unit Number is ignored if
the Command Descriptor Block is preceded by an IDENTIFY Message.
Logical Block
Address
Commands that require additional parameter data specify the length of
the Logical Block Address that is needed. See the specific command
descriptions for more detailed information.
The drive does not support Relative Addressing: it defaults to a value
of 0 which specifies that the Logical Block Address specifies the first
logical block of a range of logical blocks to be operated on by the
command. Relative Addressing indicates a technique used to
determine the next Logical Block Address to be operated on.
Transfer Length The transfer length field normally specifies the number of blocks to be
transferred between the initiator and the drive. For several commands,
the transfer length indicates the number of bytes (not blocks) to be sent.
For these commands, this field may be identified by a different name.
Parameter List
Length
The Parameter List Length is used to specify the number of bytes sent
during the DATA OUT phase. This field is typically used for
parameters that are sent to a drive (for example, mode, diagnostic, and
log parameters). A parameter list length of 0 indicates that no data is to
be transferred.