Quantum LTO 4, User Manual

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SCSI Commands: 14BSCSI Command Descriptor Blocks Page 24
Byte
Bits
7 6 5 4 3 2 1 0
8 Command Dependent
9 Control
SCSI 12-byte Command Descriptor Blocks are arranged in the format shown in the
following table.
Byte
Bits
7 6 5 4 3 2 1 0
0 Operation Code
1 Ignored LUN Service Action
2 Command Dependent
3 Command Dependent
4 Command Dependent
5 Command Dependent
6 Command Dependent
7 Command Dependent
8 Command Dependent
9 Command Dependent
10 Command Dependent
11 Control
Field names that are centered represent fields that are at least one byte long. Field
names that are left aligned with a bit number are one or more bits long. The length is
indicated by the beginning of the following field name, and by the Bits column in the
Field Descriptions table on the following page.
3.2.1.1 SCSI Command Descriptor Block Field Descriptions
Field Byte Bits Description
Operation
Code 0 The Operation Code is made up of the Group Code and the
Command Code. See Operation Code Format, below.
Ignored
Logical
Unit 1 5-7 The LUN field is vestigial from the SCSI-1 standard and is ignored.
Service
Action 1 0-4 Value identifying a function to be performed under the more general
command function specified in the OPERATION CODE field.
Command
Dependent 12-4
2-8
2-8
0-4 See the specific command.
Reserved All reserved bits must be 0.
Control Last The Control byte is made up of the Vendor Unique, Flag and Link
bits. See Control Format, below.
Fields that are one byte or longer have no entry in the Bits column.