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SCSI Interface Product Manual, Rev. J
5.34
Request Sense command (03h)
The Request Sense command (Table 151) requests that the drive transfer sense data to the initiator in the for-
mat shown in Table 152. The sense data shall be valid for a Check Condition status returned on the prior com-
mand. This sense data shall be preserved by the drive for the initiator until retrieval is requested by the initiator
when it sends the Request Sense command or until the receipt of any other command for the same drive from
the initiator that issued the command that resulted in the Check Condition status. Sense data shall be cleared
upon receipt of any subsequent command to the drive from the initiator receiving the Check Condition status.
If a drive sends a Check Condition status as a response to a Request Sense command being in error, it shall
do so only if the error was a fatal error. For example:
• The drive receives a nonzero reserved bit in the command descriptor block.
• An unrecovered parity error occurs on the Data Bus.
• A drive malfunction prevents return of sense data.
Table 151:
Request Sense command (03h)
7
Bit
Byte
0
0
1
0
Logical Unit Number
2
0
3
0
4
Allocation Length in Bytes
5
0
Notes.
[1]
See "Control byte," paragraph 4.2.6.
If any nonfatal error occurs during execution of Request Sense, the drive shall return sense data with Good
status. Following a fatal error on a Request Sense command, sense data may be invalid.
The Allocation Length in byte four of the format shown specifies the number of bytes the initiator has allocated
for returned sense data. The Allocation Length should always be at least 18 bytes for drive devices for the initi-
ator to receive all of the drive sense data. Any other value indicates the maximum number of bytes that shall be
transferred. The drive shall terminate the Data In phase when allocation length bytes have been transferred or
when all available sense data have been transferred to the initiator, whichever is less. The drive always returns
sense data in the Extended Sense Data Format.
6
5
0
0
0
0
0
0
0
0
0
0
4
3
0
0
0
0
0
0
0
0
0
0
2
1
0
1
0
0
0
0
0
0
0
Flag [1]
Link [1]
191
0
1
0
0
0
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