Section 5
SCSI Programming Guidelines
5.7.1.2
Logical Unit Number (LUN)
The Logical Unit Number for the ProDrive is zero. The LUN
is
found
in
two places: bits 5-7
of
byte 1
of
the Command Descriptor Block and bits 0-2
of
the IDENTIFY message field. (See Section 5.6.2.) The
LUN field in both the COB and IDENTIFY message field must be zero.
If
a LUN other than zero
is
specified in any command except INQUIRY and REQUEST SENSE, the command will be rejected with a
CHECK
CONDITION status and the sense key set to ILLEGAL REQUEST - Invalid LUN.
5.7.1.3 Logical Block Address (LBA)
The 21-bit (or 32-bit) Logical Block Address signifie.s the first or starting block
of
an operation. A Logical
Block can be 512,
1024,
or
2048 bytes
in
length. The MODE SELECT command
is
used to configure the
Block Length. Each
ProDrive is configured with a Logical Block Length
of
512 bytes.
5.7.1.4
Transfer or Allocation Length
The transfer length in blocks, or the allocation length in bytes, is the number
of
blocks or bytes or data to
be transferred for a single command.
• For six-byte commands, acceptable values are
OO-FFH'
For block lengths, a value ofOOH transfers
256 blocks.
See allocation byte lengths under specific commands.
• For 10-byte commands, acceptable values are
OOOO-FFFFH'
A value
of
~
transfers no blocks.
5.7.1.5
Vendor UniQue (VU)
Vendor unique bits allow for slight command modifications or special conditions to be selected. Vendor
unique bits are to
be filled with zeros.
5.7.1.6
Reserved
(R)
These bits are reserved and must be set to zero by the initiator.
5.7.1.7 Flag (F)
If
the link bit (5.7.1.8) is zero, the flag bit must be zero. Suppose the link bit
is
one.
If
the flag bit is
zero, the target sends the LINKED COMMAND COMPLETE message when the command terminates;
if
the flag bit is one, it sends the LINKED COMMAND COMPLETE (WITH FLAG) message.
5.7.1.8 Link (L)
If
the link bit is one, when the command terminates, the ProDrive sends one
of
the two messages defined
by the flag bit (above). In addition, the
ProDrive does not go to Bus Free, but immediately goes to the
Command
Out phase.
If
the link bit is zero, the ProDrive sends the normal COMMAND COMPLETE
message.
5.7.1.9 Relative Address (BELAQR)
This bit is found only in 10-byte commands (opcodes 20H - 3FH) and is not supported by the ProDrive
40S/80S.
NOTE:
If
the reserved bits
of
the IDENTIFY message or the vendor unique, reserved or relative address bits
of
the COB are non-zero, a CHECK CONDITION status
is
returned with the sense key set to
ILLEGAL
REQUEST and sense code set to Illegal use
of
bit
or
byte in COB
or
IDENTIFY
message.
5·16
SCSI Programming Guidelines
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