Fujitsu MAX3073NC - SCSI,80, Dell DC961,Hard Drive Scsi Logical Interface Specifications page 21

(1) Operation code
Bit 7 6
Group Code
The leading byte of all CDBs shows the format and type of command to be executed.
a. Group code
The group code specifies the number of bytes and format of the CDB. The groups of commands
shown below are used in the IDD.
•
Group 0 ("000"):6-byte CDB (Shown in Figure 1.1)
•
Group 1 ("001"):10-byte CDB (Shown in Figure 1.2)
•
Group 2 ("010"):10-byte CDB (Shown in Figure 1.2)
•
Group 3 ("011"):Reserved Operation Code (Shown in (6))
•
Group 4 ("100"):16-byte CDB
•
Group 5 ("101"):12-byte CDB (Shown in Figure 1.3)
•
Group 6 ("110"):Vendor unique code (Shown in Section 1.7.3)
•
Group 7 ("111"):Vendor unique code (Shown in Section 1.7.3)
b. Command code
Command code specifies the type of command in each group.
(2) LUN (Logical Unit Number)
This field specifies the address of the logical unit (device) connected under the TARG in cases where the
IDENTIFY message is not used. If the IDENTIFY message is used, the value of the CDB's LUN field is
ignored when the LUN is specified.
Note:
It is possible that the definition of this field may be changed in future SCSI standards. It is
recommended that the LUN be specified using the IDENTIFY message, and that a zero be specified
in this CDB field.
(3) Logical block address
This field shows the leading logical data block address of the data block on the disk media to be
processed by the command. In the group 0 CDB, 21-bit block addressing is possible and in the group 1,
group 2 and group 5 CDBs, 32-bit block addressing is possible. Specifications for logical data block
addressing in the IDD are described in Section 1.8.
C141-C010
5 4 3
Command Code
1.1 Command Format
2 1 0
1-3