
Bytes 7–8
The
transfer length specifies the number of contiguous
logical blocks of data to be transferred. A transfer length
of 0 means that no logical blocks are to be transferred. This
condition is not considered an error. Any other value indi-
cates the number of logical blocks to be transferred.
3.5.3
Write Extended command (2A
H
)
When the drive receives the Write Extended command, the drive writes
the data from the initiator to the disc. This command is like the Write
command, except that the command descriptor block for this command
contains a 4-byte logical block address and a 2-byte transfer length. For
more information about the Write command, see Section 3.4.7.
If there is a reservation access conflict, this command terminates with a
reservation conflict status and no data is written. 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
1
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 write the data sent by the initiator, even
if the data could be stored in the cache. If the FUA bit is
zero, the drive can write the data to 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.
64
ST3655 Family SCSI Drives Product Manual, Rev. A
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