Section 5
SCSI Programming Guidelines
NUMBER
OF
BLOCKS (Bytes 1-3) - Specifies the number
of
logical blocks on the
medi~m
that meet the density code and block length
in
the
block descriptor. A value of zero indicates that all
remaining logical blocks
of
the drive
have
the
medium
characteristics specified
by
the
block descriptor.
Any non-zero value within the capacity of the
ProDrive can
be
used
to
limit access
of
the drive
to
a
certain number
of
blocks.
BLOCK LENGTH (Bytes 5-7) - The block length specifies the length
in
bytes
of
each logical
block described
by
the
block descriptor. For
the
ProDrive
, allowable values are 512 (200H)'
1024
(400H)'
or
2048
(800H)' The default block length
is
512 (200H)'
NOTE: The block length may
be
altered without reformatting the drive or affecting stored data.
PAGE
DESCRIPTOR(S):
PAGE CODE (Byte 0, Bits 5-0) - Pages are optional; they
may
be included
in
any order,
immediately following the block descriptor. The mode parameters
are divided into pages to avoid
having to specify all Mode
Parameters each time a MODE SELECT command
is
issued. A page
is
the minimum unit that can
be
specified
in
a MODE SELECT or MODE SENSE command. Each
time a page
is
referenced,
all
parameters
on
that page must
be
specified. Changeable parameters
may
be
set to
any
acceptable values; non-changeable parameters must
be
set
to
zero.
The pages
are
numbered for reference.
Each
page
contains parameters grouped
by
functionality. For
example,
Page
1 contains the Read/Write Error Recovery Parameters. These are the parameters which
determine drive behavior during a data handling error.
The
Retry Count Parameter
is
located
on
this
page, as are the bits which tum on/off error
detection~
and determine if soft errors are reported.
The
ProDriv~
supports the
foUowing
pages:
Page
OIH
02H
03H
04H
37H
39H
Description
Read/Write Error
Recovery
Parameters
Disconnect/Reconnect Control Parameters
Direct Access Device Format Parameters
Rigid Disk Drive Geometry Parameters*
Quantum Unique Control Parameters
Quantum Unique Drive Control Parameters
* Read-only. Can only be referenced via
the
MODE
SENSE command.
PAGE LENGTH (Byte
I)
- Indicates
the
number
of
bytes
of
the page that will
follow~
beginning
with the first byte
of
flags or values
and
continuing consecutively. The page length must be set
to
the value returned
by
the ProDrive
in
the MODE SENSE Page Length byte. Otherwise, a CHECK
CONDITION status with a sense key
of
ILLEGAL REQUEST will result.
SCSI Programming Guidelines
5·43
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