HP C2246 Technical Reference Manual page 116

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.O (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
•
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
approted by Hewlett-Packard may be deemed a violation of warranty.
Write Buffer Command Descriptor Block (COB}
Bit
7
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=OS)
Control Byte
Mode. Modes 0, 4, and 5 are supported:
Mode 0 (OOOb ): Write combined header and data.
Mode 4 (lOOb ): 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-60 SCSI Command Descriptions