CDU-541
CD-ROM
DRIVE
SCSI
INTERFACE
MANUAL
5 . 2 • 36. WRITE BUFFER Command
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Bit
I
Byte
I
7
6
5
4
3
2
1
o
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o
I
I
Operation
Code (3Bh)
-----1-----------------------------------------------------------------------
1 I
Logical
Unit
Number
:
Reserved
:
Mode
-----1-----------------------------------------------------------------------
2 :
Reserved
3
(MSB)
4
Buffer
Offset
5
(LSB)
-----1-----------------------------------------------------------------------
6 I
(MSB)
-----+---
---I
7 I
Transfer
Length
I
-----1--- ---I
8 I
(LSB)
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-----1-----------------------------------------------------------------------1
9 I
Control
Byte
I
==============================================================================
The
WRITE
BUFFER
command
is
used
in
conjunction
with
the
READ
BUFFER
command
as
a
diagnostic
function
for
testing
controller
memory
and
the
bus
integrity.
This
command
will
not
alter
the
medium.
The
function
of
this
command
and
the
meaning
of
fields
within
the
command
descriptor
block
depend on
the
contents
of
the
mode
field.
A
mode
field
value
of
zero
indicates
that
the
buffer
offset
is
zero.
A
mode
field
value
of
one
indicates
that
the
buffer
offset
is
valid
and
the
data
will
be
placed
in
the
buffer
with
that
offset.
The
buffer
offset
is
the
byte
offset
within
the
buffer
where
the
data
will
be
stored.
If
the
controller
is
unable
to
accept
the
specified
buffer
offset,
it
will
return
CHECK
CONDITION
status.
The
sense
key
is
set
to
ILLEGAL
REQUEST
and
the
additional
sense
code
is
set
to
ILLEGAL
VALUE
IN
CDB.
The
data
to
be
transferred
is
preceded
by
a
four-byte
header.
The
header
consists
of
all
reserved
bytes.
The
transfer
length
specifies
the
maximum
number
of
bytes
that
will
be
transferred
during
the
DATA
OUT
phase.
This
number
includes
four
bytes
of
WRITE
BUFFER
header,
so
the
data
length
to
be
stored
in
the
controller's
buffer
is
transfer
length
minus
four.
If
the
transfer
length
minus
four
exceeds
the
capacity
of
the
buffer
the
controller
will
return
a
CHECK
CONDITION
status.
The
sense
key
is
set
to
ILLEGAL
REQUEST
and
the
additional
sense
code
is
set
to
ILLEGAL
VALUE
IN
CDB.
5-63
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