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8.1 SCSI Control Byte
The Control Byte is the last byte of every CDB. The format of this byte is shown below.
7
6
VU = 0
Figure 49. SCSI Control Byte
VU
VU stands for Vendor Unique.
FLAG
The Flag bit specifies which message the drive shall return to the initiator if the link bit is one
and the command completes without any error. If Link is zero, Flag must also be zero. If Link is
one and the command terminates successfully, the drive will send either the LINKED
COMMAND COMPLETE message (FLAG=0) or the LINKED COMMAND COMPLETE WITH
FLAG message (FLAG=1). Typically this bit is used to cause an interrupt in the initiator be-
tween linked commands.
LINK
This bit is set to one to indicate that the initiator desires an automatic link to the next command
upon successful completion of the current command. Upon successful completion of the
command, the drive will return INTERMEDIATE GOOD status and then send one of the two
messages defined under Flag above.
Upon unsuccessful completion of the command, the drive will return CHECK CONDITION
status or RESERVATION CONFLICT status and then send the COMMAND COMPLETE
message. No further commands in the chain are executed.
8.2 Abbreviations
These abbreviations are used throughout the following sections:
CDB
Command descriptor block
LBA
Logical Block Address
LSB
Least significant bit
LUN
Logical Unit Number. An encoded three-bit identifier for the logical unit
MSB
Most significant bit
RSVD
Reserved
VU
Vendor unique bits
8.3 Byte ordering conventions
In this specification, where it is not explicitly stated, all multibyte values are stored with the most significant
byte first. For example, in a 4-byte field byte 0 will contain the MSB and byte 3 the LSB.
Bit
5
4
3
Reserved = 0
Ultrastar 146Z10 hard disk drive specifications
2
1
0
FLAG
LINK
50
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