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Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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Table 4.2-3. Typical Command Descriptor Block for Ten Byte Commands
Bit
7
6
5
4
3
2
1
0
Byte(s)
0
Operation Code
1
Logical Unit No.
Reserved
Rel
0
0
0
Adr
2
Logical Block Address(if required)(MSB)
3
Logical Block Address (if required)
4
Logical Block Address (if required)
5
Logical Block Address (if required)(LSB)
6
Reserved
7
Transfer Length (if required)(MSB) [1]
8
Transfer Length (if required)(LSB) [1]
9
Control Byte [1]
[1] For Twelve byte commands there are two more bytes of transfer length, bytes 9 and 10, and the control
byte is byte 11.
4.2.2
Logical Unit Number (LUN)
The logical unit number (LUN) addresses one of up to eight physical devices or virtual devices attached to a
target. The only valid LUN number for the disc drives supported by this manual is Zero.
The LUN in the CDB is provided for systems that do not implement the Identify Message. If an Identify
message is sent to the disc drive, the disc drive will use the LUN number specified in this message. In this
case, the disc drive shall ignore the LUN specified within the command descriptor block.
The disc drive will reject commands that select an invalid LUN (except Request Sense and Inquiry) by
requesting and accepting the command bytes, then going to Status phase and sending Check Condition
status. Note that the LUN is sent in the LUN field of a CDB (if no Identify message has been received for this
selection) or by the LUN field of an Identify message.
Request Sense commands selecting an invalid LUN will receive a Sense Data block with the Illegal Request
Sense Key and an Invalid LUN Error Code. Inquiry commands will return Inquiry Data with the Peripheral
Device Type field set to Logical Unit Not Present (7Fh). Request Sense and Inquiry commands will not send
Check Condition status in response to an invalid LUN selection.
