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4.2 Data Access Commands
C141-C013 215
4.2.2 READ EXTENDED (28)
Bit
Byte
7 6 5 4 3 2 1 0
0 X'28'
1 0 0 0
×
FUA 0 0 0
2 Logical Block Address (MSB)
3 Logical Block Address
4 Logical Block Address
5 Logical Block Address (LSB)
6 0 0 0 0 0 0 0 0
7 Transfer Block Count (MSB)
8 Transfer Block Count (LSB)
9 0 0 0 0 0 0 0 0
This command reads the number of blocks of data in continuous logical data
blocks specified in the "Transfer block count" field with the logical data block on
the disk media specified in the "Logical block address" field in the CDB as the
top.
The functions of this command are the same as those of the Group 0 READ
command (Section 4.2.1) with the exception that it is possible to specify 4-byte
logical block addresses and 2-byte transfer block counts. However, when zero is
specified for the "Transfer block count," the command is terminated normally
without seek and pre-fetch being performed.
• FUA (force unit access)
When this bit is "0", it indicates that the HDD satisfy the command by
accessing the cache memory. Any logical blocks that are contained in the
cache memory may be transferred to the INIT directly from the cache
memory.
When this bit is "1", it indicated that the HDD shall access the media in
performing the command prior to returning GOOD status. READ commands
shall access the specified logical blocks from the media (i.e., the data is not
directly retrieved from the cache).