Request Sense
The
REQUEST
SENSE command requests
that
the
Target transfer sense
data
to
the
Initiator. Only
the
extended sense
data
format is supported.
Request Sense Command Descriptor Block (CDB)
Bit
Byte
7
I
6
I
5
. I
4
I
3
I
2
I
1
I
0
00
Opcode
= 03H
01
Logical
Unit
Number
1
Reserved
02-03
Reserved
04
Allocation
Length
05
Control
Byte
The
returned Request Sense
data
is valid for a CHECK CONDITION
status
returned on
the
prior
command~
This
data
is
preserved by
the
Target for
the
Initiator
until retrieved by
the
REQUEST
SENSE command or until
the
receipt of any other command for
the
same logical
unit from
the
Initiator
that
issued
the
command resulting in
the
CHECK
CONDITION
status.
Sense
data
is cleared upon receipt of any subsequent command
to
the
logical unit from
the
Initiator
receiving
the
CHECK CONDITION status.
In
the
case
of
the
single
Initiator
option,
the
Target will assume
that
the
REQUEST
SENSE command is from
the
same
Initiator.
Sense information will be cleared by
the
REQUEST SENSE command following
the
transfer of
the
data.
AUo~ation
Length. This field specifies
the
number of bytes
that
the
Initiator
has allocated
for returned sense
data.
In
the
SCSI (CCS) mode, an allocation length of zero (0) indicates
that
four bytes of sense
data
will be transferred. In
the
SCSI-2 mode, an allocation length
of zero
(0) indicates
that
no
data
will be returned. Any other value indicates
the
maximum
number of bytes
that
will be transferred.
The
Target will
terminate
the
Data
In phase when
the
specified number of bytes have been transferred or when all available sense
data
has been
transferred
to
the
Initiator, whichever is less. The drive will
return
a maximum
of
22 bytes
(SCSI-CCS) or 28 bytes (SCSI-2) of sense
data.
Refer
to
the
REQUEST
SENSE Extended
Data
Format descriptions.
The
REQUEST
SENSE command will
return
the
CHECK CONDITION
status
only
to
report
fatal errors for
the
REQUEST SENSE command.
The
REQUEST SENSE command will be
executed even
if
the
drive is reserved
to
another Initiator.
If
any nonfatal error occurs during
the
execution of
the
REQUEST SENSE command,
the
Target will
return
the
sense
data
with GOOD
status.
When a fatal error occurs on a
REQUEST
SENSE command,
the
returned sense
data
may be invalid.
After
the
Sense
Data
is returned, all conditions are cleared except for a UNIT
ATTENTION
Sense Key if
Power~On
verification failed.
In
this case, the HARDWARE
ERROR
Sense Key
is set by
the
Target for
the
first REQUEST SENSE,
and
UNIT ATTENTION is set for
the
subsequent command. This is done
to
insure
that
diagnostic failures
and
"Reset Conditions"
are observed.
A·42 SCSI Command Descriptions
DRAFT
1/18/93 09:58
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