HP C2488A Technical Reference Manual page 98

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