Mode Sense (10) - 5Ah

The library will return the current settings for the supported mode pages. This command can only be issued to the controller device logical unit.

This command can be used to determine certain operational settings governing the behavior of the library. Use of MODE SENSE to obtain these parameters during initialization is highly recommended to facilitate the most flexibility in supporting the library.

The ten-byte MODE SENSE CDB format is shown in the following table.

Table 1: MODE SENSE CDB format

Bit Byte	7	6	5	4	3	2	1	0
0	Op Code (5Ah)
1	Logical Unit Number			Rsvd	DBD	Reserved
2	PC		Page Code
3	Reserved
4	Reserved
5	Reserved
6	Reserved
7	Allocation Length
8
9	Control

Field	Description
Disable Block Descriptors (DBD)	A value of 0 or 1 is supported, although block descriptors are not returned.
Page Control (PC)	This field indicates the type of mode page parameter values to return as shown in the following table. See Table 2.
Page Code	This field determines which pages should be reported. A list of the supported pages is shown in the previous table.
Allocation Length	This field specifies the number of bytes that the initiator allocated for returned MODE SENSE data. A length of 0 means that the library will return no MODE SENSE data. This is not considered to be an error.

Table 2: Page Control (PC) field

Page Control		Description
0	0	Report current values defined by: The values set by the last successful MODE SELECT command. The default values if no saved values exist.
0	1	Report changeable values.
1	0	Report default values.
1	1	Report saved values (report default values if no pages are previously saved).

Note: Although the library may support changes for various mode parameters via the library user interface configuration settings, a mode parameter will be reported as non-changeable if not supported to be changeable via SCSI control.

The ten-byte MODE SENSE response consists of a single eight-byte Mode Parameter Header, followed by zero or more mode pages. Each page is individually described in “Mode Pages.”

Mode Parameter Header

The following table shows the format of the Mode Parameter Header for the ten-byte MODE SENSE command.

Table 3: Mode Parameter Header format for Mode Sense (10)

Bit Byte	7	6	5	4	3	2	1	0
0	Mode Data Length
1
2	Reserved
3	Reserved
4	Reserved
5
6	Reserved
7

Field	Description
Mode Data Length	This specifies the length in bytes that is available to be transferred as part of the response. The Mode Data Length does not include itself but does include the remaining six bytes of the parameter header, as well as the overall total number of bytes being