Write Buffer
The
WRITE
BUFFER
command puts
data
into the Target's buffer RAM without writing
to
the
disk. An Initiator can use this command in conjunction with
the
READ
BUFFER
command
to
check
the
SCSI interface and
the
buffer RAM. Only mode 0 (zero) of
the
WRITE
BFFER
command is used for this purpose.
The download microcode function
is
implemented with modes 4 and 5.
Mode 4 writes a partial segment of the microcode without attempting
to
execute
that
microcode. Mode 4
is
useful for Initiators which do not have a large enough buffer size
to
download microcode in one segment.
Mode 5 is used for the last (or only) segment of
the
microcode.
The
Target executes its
Power-On sequence after writing microcode in mode 5.
Caution
I
Byte
00
01
02-05
06-08
09
The
WRITE
BUFFER
download microcode mode command allows
the
Initiator to execute code
that
may cause damaging results.
It
should only
be performed when no
data
retention
is
required.
Use
of this command
should be restricted
to
development or other highly controlled environments.
Development of the code for this command should be carefully coordinated
with
the
product's support team. Execution of this command with code
not
approved
by
Hewlett-Packard may be deemed a violation of warranty.
Write Buffer Command Descriptor Block (COB)
Bit
'1
I
6
I
5
I
4
I
3
I
2
I
1
I
0
Opcode
=
3BH
Logical
Unit
Number
I
Reserved
I
Mode
Reserved
(MSB=06)
Byte
Transfer
Length
(LSB=08)
Control
Byte
Mode. Modes 0, 4, and 5 are supported:
Mode
0
(OOOb):
Write combined header and data.
Mode 4
(100b): Download microcode.
Mode 5
(101b): Download microcode and save.
Byte Transfer Length. This field specifies
the
number of bytes to be transferred
to
the Target
during
the
data
phase. The transfer length includes the number of bytes
to
be written
to
the
data
buffer plus four (4) for the header. (The four header bytes are ignored by
the
Target and
not written
to
the
buffer.) A transfer length of zero indicates
that
no
data
transfer will take
place
and
will not be considered an error.
It
is
not considered an error to request a transfer
length smaller
than
the
Target
data
buffer size.
If
the
transfer length
is
greater
than
the maximum size of the Target's
data
buffer,
the
data
phase will not be performed. The Target progresses immediately to the
Status
phase with
CHECK CONDITION, ILLEGAL REQUEST Sense
Key.
A-50 SCSI Command Descriptions
DRAFT
1/18/93 09:58
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