Section 5
SCSI
Programming Guidelines
The ProDrive will execute any
of
the above commands after a delay
of
one second, maximum, following
application
of
power to the drive. They will not return CHECK CONDITION status with the NOT
READY sense key even
if
the drive
is
not ready. All other commands could require disk access. (Refer to
START/STOP UNIT command, Section 5.11.14 below.)
5.11.2
REZERO UNIT COMMAND: OPCODE =
01
(hex)
The REZERO UNIT command (Table 5-9) requests that the drive actuator be repositioned to cylinder zero
and head zero.
TABLE
5-9
REZERO
UNIT
Command
Bit 7 6
5
4
3
2
1 o
Byte
0
OPCODE=OIH
1
LUN=O
I
RESERVED = 0
2-4
RESERVED
=0
5
VU=O
I
RESERVED=O
I
F
I
5.11.3
REQUEST SENSE COMMAND: OPCODE = 03(hex)
5.11.3.1 Command Structu
re
The REQUEST SENSE command (Table 5-10) requests that the sense data be sent to the initiator.
The sense data applies to the previous command from the same initiator.
Sense data is saved for an
initiator until it is retrieved by that initiator
or
until another command
is
received from that initiator.
Commands from any initiator will not alter the sense data saved for
other initiators.
TABLE
5-10
REQUEST
SENSE
Command
L
Bit
7 6
5
4
3
2 1 o
Byte
0
OPCODE=03H
1
LUN=O
I
RESERVED=O
2
-3
RESERVED
=0
4 ALLOCATION LENGTH (BYTES)
5
VU=O
I
RESERVED
=0
I
F
I
L
ALLOCATION LENGTH - specifies the maximum number
of
bytes allocated by the initiator
for returned sense
data. Acceptable values are
OO-FFH'
(A value
of
00
indicates that four bytes
of
data will
be
returned.) The ProDrive will terminate the DATA IN phase when the allocated number
of
bytes have been transferred
or
when all available sense data have been transferred to the initiator,
whichever is less.
For
the ProDrive. an allocation length
of
18
(l2H)
is
recommended.
5·22
SCSI Programming Guidelines
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