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Page 64
MODE SENSE
Command Descriptor Block
6-Byte Command Descriptor Block
The MODE SENSE command allows the host to determine various drive parameters.
These parameters are sent from the drive to the host as data formatted in a
parameter list. This command is complementary to the Mode Select command that
sets device parameters.
The drive terminates execution of the Mode Sense command:
•
When the number of bytes specified in the Allocation Length field have been sent
to the host, or
•
When all available Mode Sense data has been sent to the host.
If a Mode Select command has not been performed since power-on or SCSI Reset,
the default mode parameters are in effect.
All Mode Select parameters may be rounded up or down, as appropriate. A Mode
Sense command may be issued after a Mode Select command to determine which
parameters have been rounded.
Block and page descriptions for this command are shown below and on subsequent
pages.
Bits
Byte
7
6
0
1
Ignored LUN
2
PC
3
4
5
Field Descriptions
Field
Bytes
Bits
Operation
0
Code
Ignored
1
5-7
Logical
Unit
DBD
1
3
5
4
3
Operation Code (1Ah)
Reserved
DBD
Page Code
Reserved
Allocation Length
Control
Description
The Operation Code for the 6-byte version of Mode Sense is 1Ah.
The LUN field is residual from the SCSI-1 days and is ignored.
0 = Return the block descriptor in the Mode Sense data.
1 = Disable Block Descriptors (DBD).
NOTE: When the DBD is 1, the Block Descriptor Length in the pa-
rameter header is 0.
LTO SCSI Interface Manual
2
1
0
Reserved
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