Section 5 SCSI Programming Guidelines
5.11.23
WRITE BUFFER COMMAND: OPCODE = 3B(hex)
The WRITE BUFFER command (Table 5-42) is used
in
conjunction with the READ BUFFER command
as a diagnostic function for testing the target memory and the
SCSI bus integrity. This command will not
alter the medium.
TABLE
5-42
WRITE
BUFFER Command
Bit 7
6 5
4
3
2 1
Byte
0
OPCODE=3BH
I LOGICAL UNIT NUMBER
I
RESERVED
=0
I
MODE
2
BUFFERID=O
3-5 RESERVED
=0
6-8
(MSB)
TRANSFER LENGTH
9
CONTROL BYTE
BUFFER
ID
(Byte 2) - Must
be
be set to zero. Any other Buffer ID code will result in a
CHECK CONDITION status with a sense key
of
ILLEGAL REQUEST (05H)'
o
(LSB)
TRANSFER
LENGTH
(Bytes 6-8) - Specifies the maximum number
of
bytes that are to be
transferred during the DATA OUT phase.
The function
of
this command and the meaning
of
the transfer length field depend on the contents
of
the
mode field. The mode field is defined as follows:
Bit2
BiU
BitO
MODE
0 0 0 Write combined header and data
o.
0 I Vendor unique
0
1 0 Write data
0
1 I Reserved
I 0
0
Not supported
1 0
I
Not supported
I 1 0 Reserved
I 1 I
Reserved
5.11.23.1 COMBINED HEADER ANP
pArA
Mode
(OOOBl
In this mode,
data
to
be
transferred is preceded by a four-byte header which contains all reserved bytes.
These four bytes
of
header must be accounted for in the specified transfer length (bytes 6-8); the amount
of
data to
be
stored in the ProDrive buffer is the transfer length minus four. The initiator should attempt to
ensure that the transfer length is not greater than four plus the available length returned in the header
of
the
READ BUFFER command (mode
000s).
If
the transfer length exceeds this amount, the ProDrive will
return CHECK CONDITION status with the sense key
of
ILLEGAL REQUEST (05H)'
5·66
SCSI
Programming
Guidelines
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