Seagate ST3285N, Product Manual

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3.5.2 Read Extended command (28
H
)
When the drive receives the Read Extended command, it transfers data
to the initiator. This command is the same as the Read command
discussed in Section 3.4.6, except that in the CDB for the Read Extended
command, a 4-byte logical block address and a 2-byte transfer length
can be specified.
If there is a reservation access conflict, this command terminates with a
reservation conflict status and no data is read. For more information
about the reservation conflict status, see Section 3.2.
Bit
Byte
7 6 5 4 3 2 1 0
0 0 0 1 0 1 0 0 0
1 LUN DPO FUA 0 0 Rel Adr
2–5 Logical block address
6 0 0 0 0 0 0 0 0
7–8 Transfer length
9 0 0 0 0 0 0 Flag Link
Byte 1 If the DPO (disable page out) bit is one, the cached data
that the drive receives during this command has the lowest
priority for being retained in the cache. If DPO is zero, the
cached data has the highest priority for being retained in
the cache.
If the FUA (forced unit access) bit is one, the drive must
access the disc to get the data requested by the initiator,
even if the data is available in the cache. If the FUA bit is
zero, the drive can get the data from the cache or the disc.
If the
REL ADR bit is one, the logical block address field
specifies the first logical block of the range of logical blocks
to be written and verified by the drive. If the REL ADR bit is
one, the logical block address field is a two’s complement
displacement. This displacement is added to the logical
block address last accessed on the drive to determine the
logical block address for this command. The REL ADR bit
should only be one if linked commands are used.
Bytes 2–5 The logical block address specifies the logical block where
the read operation begins.
ST3655 Family SCSI Drives Product Manual, Rev. A 63