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Sony CDU-541 - Command Descriptor Block (CDB)

Sony CDU-541
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COU-541
CD-ROM
DRIVE
SCSI
INTERFACE
MANUAL
4
.2.
CollUlland
Descriptor
Block
The
Command
Descriptor
Block
(COB)
is
a
packet
of
six
or
ten
bytes
sent
from
the
host
computer
during
a
command
phase
that
requests
the
controller
to
__
--
perform
some
operation.
The
common
parts
of
the
COB
are
described
here.
4.2.1.
Operation
Code
The
operation
code
is
the
first
byte
of
the
COB
and
indicates
whether a
six
or
ten
byte
is
being
sent.
Each
command
has
a
unique
operation
code.
4.2.2.
Relative
Address
Bit
The
relative
address
bit
is
applicable
to
some
ten
byte
commands.
This
version
of
the
controller
does
not
implement
relative
addressing.
4.2.3.
Starting
Logical
Address
The
starting
logical
address
specifies
the
logical
block
at
which
the
requested
read,
verify
or
play
operation
is
to
begin.
Not
all
COB's
have
starting
logical
addresses.
4.2.4.
Transfer
Length
The
transfer
length
specifies
the
number
of
logical
blocks
to
be
transferred.
A
transfer
lengt~
value
of
zero
has
special
meaning
in
some
commands. The
size
of
the
logical
blocks
can
be
set
using
the
MODE
SELECT
command.
4.2.5.
Parameter
Length
The
parameter
length
specifies
the
exact
number
of
bytes
of
sense
data
that
the
host
will
transfer
to
the
controller.
4.2.6.
Allocation
Length
The
allocation
length
specifies
the
maximum
number
of
bytes
that
the
initiator
has
allocated
for
returned
sense
data.
An
allocation
length
of
zero
indicates
that
no
sense
data
will
be
transferred.
This
condition
will
not
be
considered
as
an
error.
The
controller
will
terminate
the
DATA
IN
phase
when
allocation
length
bytes
have
been
transferred
or
when
all
available
sense
data
have been
transferred
to
the
initiator,
whichever
is
less.
4-4

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