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M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS
April 1997 CG00000-011503 REV. A 4-57
The Page Code allows the initiator to select any one specific page or all of the pages supported by
a target. Pages are used to set and return device parameters. If the initiator uses a page code value
not implemented by the target, the target will return CHECK CONDITION status with sense key
set to ILLEGAL REQUEST, and additional sense code to INVALID FIELD IN CDB.
The Allocation Length specifies the number of bytes the initiator has allocated for returned Mode
Sense data. An Allocation Length of 0 indicates no Mode Sense data is to be transferred. This con-
dition is not considered an error. Any other value indicates the maximum number of bytes trans-
ferred. The target terminates the DATA IN phase when allocation length bytes have been
transferred or when all available Mode Sense data have been transferred to the initiator, whichever
is less.
4-3.13.2 Mode Sense Data
The MODE SENSE data contains a four-byte header, followed by 0 or one eight-byte block
descriptors, followed by zero or more variable length pages.
Mode Sense Data Header:
Table 4-52. PC Field
PC FIELD
BITS DESCRIPTION
7 6
0 0
Report Current Values:
The current values are those parameters under which the target is presently con-
figured. The current values are defined to be the following:
1. those values set in the last successfully completed MODE SELECT command,
2. saved values if a MODE SELECT hasn’t successfully completed since the last power-on, hard reset
condition, or BUS DEVICE RESET message, or
3. default values if saved values are not available.
Page fields not supported are set to zero. The additional page length field returned by the target indicates
the number of bytes supported in that page.
0 1
Report Changeable Values:
The changeable values of any page indicate which parameters the initiator
may change by a subsequent MODE SELECT command. Any field allowed to change is set to all ones.
Fields and bits not allowed to be changed by the initiator are set to zero. Attempting to change any field,
via the MODE SELECT command, that is not changeable causes the target to return a CHECK CONDI-
TION status with the sense key set to ILLEGAL REQUEST in the sense data. In this case, no parameters
in that page are changed. The additional page length field of each page returned by the target indicates the
number of bytes which are supported for that particular page.
1 0
Report Default Values:
The target returns to the initiator the field values set to the target’s or LUN’s
default values. The additional pages length field of each page returned by the target indicates the number
of bytes supported for that particular page.
1 1
Report Saved Values:
The target returns the saved values of the mode parameters. Until the first suc-
cessful MODE SELECT command is completed with the SP (Save Pages) bit set to 1, the default values
will be returned for this PC field setting.
Table 4-53. MODE SENSE Data Header
BITS
DEFAULT
BYTES 7 6 5 4 3 2 1 0
0
MODE SENSE Data Length N.A.
1
Reserved 00h
2
WP Buffered Mode Speed =0h 90h or 10h
3
Block Descriptor Length 00h /08h