Mode Select, Mode Sense
Sense
Data
Length. This field specifies the length in bytes of the page
data
to
be returned
during the
Data
In phase. The Sense
Data
Length field does not include itself nor does
it
include the Block Descriptor length.
Media Type.
Set to all zeros
to
indicate fixed disk.
WP
(Write
Protect).
Indicates whether the drive is in the write protect mode: zero (0) =
write protect disabled; one (1) = write protect enabled. The write protect mode is enabled
or disabled with bit 7 in the Mode
Select command control byte: zero (0) = write protect
disabled; one (1)
= write protect enabled.
DPOFUA. Indicates whether the target supports
the
cache control bits DPO (Disable Page
Out)
and FUA (Force Unit Access) in the extended READ command. The
target
always
reports
a zero (0) indicating
that
only the FUA bit is supported.
Device Specific Parameters. Not used. Set
to
all zeros.
Block Descriptor Length. This field specifies the length in bytes of
the
Block Descriptor, and
does not include the
Parameter Pages. The block descriptor length will be either 0 or
8.
The
Block Descriptor specifies the media characteristics for the entire Logical
Unit.
Density Code. Not used. Set
to
zeros.
Number
of
Blocks. Set to all zeros by MODE SENSE indicating
that
all blocks are set
to
same size. In MODE SELECT, used by the Set Capacity function
to
allow
the
Initiator
to
modify the working capacity of the drive.
The
Set Capacity function is performed by placing a value in the Number of Blocks field of
the
6-
or lO-byte MODE SELECT Block Descriptor. The change
to
the working capacity of
the
drive can be made non-volatile by setting the SP (Save Page)
bit
in the MODE SELECT
Command Descriptor Block to one (1).
Considerations for setting of Number of Block field:
If
set
to
zero (0), the working capacity is not affected.
If
set
to
FFFFFFh,
the working capacity is set to maximum.
If set to a value greater than zero
(0),
but
less than'or-equal
to
the
maximum drive
capacity, the working capacity is adjusted
to
the
number of blocks indicated.
If
set
to
a value greater than
the
maximum drive capacity, the drive will set a Status of
CHECK
CONDITION, a Sense Key oflLLEGAL REQUEST, and an additional Sense Key
of ILLEGAL LOGICAL
BLOCK ADDRESS.
Attempting any access beyond the current working capacity
of
the
drive will result
in
a Status
of CHECK CONDITION, a Sense Key of ILLEGAL REQUEST, and an Additional Sense Key
of ILLEGAL LOGICAL
BLOCK ADDRESS. .
Block
Length. Indicates logical block size; Set
to
user configuration in MODE SENSE. In
MODE SELECT, changing the Block Length (or changing
the
Data
Bytes per Physical Sector
field
in
Mode Page 03H) will reset the working capacity to the maximum.
PS (Page Save). Indicates savable Mode Sense page when set
to
one (1). Ignored for Mode
Select.
Page
Length. Indicates number of bytes remaining in specified page after Page Length field.
DRAFT
SCSI
Command Descriptions A·21
1/18/93 09:58
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