Figure 5-2 Command Descriptor Block Control Field - Data Format - Quantum DLT 8000 Product Manual

SCSI Commands
Table 5–2 Command Descriptor Block — Field Descriptions (continued)
Field
Control Field
Relative Address (RelAdr)
The final byte of the CDB is called the Control byte. Its contents are defined in the next
figure and table. In the remainder of this chapter, the Flag and Link bytes will not be
redefined each time they appear as part of a command.
Bit 7
Byte
--- Unused
Figure 5–2 Command Descriptor Block Control Field — Data Format
Table 5–3 Command Descriptor Block Control Field — Field Descriptions
Field
Unused
Flag
Link
5-6
Description
The Control Field is the last byte of every command descriptor block.
Its format is shown in Figure 5–2 and it contains the Flag and Link bits.
Use of these bits is initiator-dependent. Setting the Link bit = 1
provides an automatic link to the next command, bypassing the usual
ARBITRATION, SELECTION, and MESSAGE OUT phases that would
normally occur between commands. Other bits in the Control Field are
considered to be reserved.
Must be 0 (not supported).
6 5
Description
Bits 6 & 7 of the Control Byte are reserved for vendor-specific use.
They are not used by this tape drive, so the value in each of these
bits is always 0.
The Flag bit is used in conjunction with the Link bit to notify the
initiator in an expedient manner that a command has been
completed.
A Link bit set to 1 indicates that the initiator requests continuation
of a task (an I/O process) across two or more SCSI commands.
If the Link bit is 1 and the Flag bit is 0, and the task completes
successfully, the drive continues the task and returns a status of
INTERMEDIATE and a LINKED COMMAND COMPLETE message.
If the Link bit and the Flag bit within a Control word are both set
to 1, and the drive completes a command with a status of
INTERMEDIATE, the drive returns a LINKED COMMAND COMPLETE
message (with Flag).
Quantum DLT 8000 Tape System
4 3
Reserved
2 1
Flag
0
Link