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2.1 Command Format
C141-C013 105
Table 2.3 12-Byte CDB basic format
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code
1 Reserved 0 0 0 0 0
2 Logical Block Address (MSB)
3 Logical Block Address
4 Logical Block Address
5 Logical Block Address (LSB)
6 Transfer Data Length (MSB)
7 Transfer Data Length (LSB)
8 Transfer Data Length (MSB)
9 Transfer Data Length (LSB)
10 0 0 0 0 0 0 0 0
11 Control Byte
The meanings of each of the fields in the CDB are explained below. Depending
on the type of command, the basic format of the CDB and the definition and
meaning of a field may differ. Details are described in the specifications for
individual commands in Chapter 4.
(1) Operation code
Table 2.4 Operation code
Bit 7 6 5 4 3 2 1 0
Group Code Command Code
The top byte of all CDBs shows the format and type of command that is being
executed.
a. Group code
The group code decides the number of bytes in the CDB and its format. The
HDD uses the commands of the groups shown below.
Group 0 ("000"): 6-byte CDB (Shown in Table 2.1)
Group 1 ("001"): 10-byte CDB (Shown in Table 2.2)
Group 2 ("010"): 10-byte CDB (Shown in Table 2.2)