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Table 60:
Typical variable length CDB
Bit
7
Byte
0
Operation Code (7Fh) [1]
Control [7]
1
Reserved
2
Reserved
3
Reserved
4
Encryption Identification [8]
5
Reserved
6
Additional CDB Length (n–7) [9]
7
8
(MSB)
9
10
Service Action specific fields [10]
:
n
Notes for Tables 56, 57, 58, 59, and 60.
[1]
The Operation Code field of the Command Descriptor Block contains the code value indentifying the oper-
ation being requested by the CDB. The Operation Code provides for a possible 256 command operation
codes. Details of the various commands with their operation codes are defined in Section 8.0 of this man-
ual.
[2]
Service Action. All typical CDB formats except the typical 6-byte format provide for a Service Action field
containing a coded value identifying a function to be performed under the more general command function
specified in the Operation Code field. While the Service Action field is defined for typical CDB formats, it is
used as described in this clause only in those CDB formats that explicitly contain a Service Action field.
When the specific field Service Action is not defined in a CDB format, the bits identified as the Service
Action field in a typical CDB may be used for other purposes. More details appear on this in Section 8.0
where the details of each command are described.
[3]
The Logical Block Address on logical units or within a partition on device volumes shall begin with block
zero and be contiguous up to the last logical block on that logical unit or within that partition.
A six-byte command descriptor block contains a 21-bit Parameter List Length field. The 10-byte, the 12-
byte and the 16-byte command descriptor blocks contain 32-bit Logical Block Address fields. Logical
Block Address fields in additional parameter data have their length specified for each occurrence. See the
specific command descriptions.
[4]
The Transfer Length specifies the amount of data to be transferred, usually the number of blocks. For sev-
eral commands the transfer length indicates the requested number of bytes to be sent as defined in the
command description. For these commands the transfer length field may be identified by a different name.
See the following descriptions and the individual command descriptions for further information.
Commands that use one byte for Transfer Length allow up to 256 blocks of data to be transferred by one
command. A Transfer Length value of 1 to 255 indicates the number of blocks that shall be transferred. A
value of zero indicates 256 blocks.
Commands that use two bytes for Transfer Length allow up to 65,535 blocks of data to be transferred by
one command. In this case, a Transfer Length of zero indicates that no data transfer shall take place. A
value of 1 to 65,535 indicates the number of blocks that shall be transferred.
For several commands more than two bytes are allocated for Transfer Length. Refer to the specific com-
mand description for further information.
6
5
Service Action [2]
SCSI Interface Product Manual, Rev. B
4
3
2
1
(LSB)
0
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