User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Overview of Command and Status Processing
112 Quantum DX-Series Software Interface Guide
Table 73 Command
Descriptor Block
Control Field - Data
Format
Bit/Byte 7 6 5 4 3 2 1 0
5
Allocation Length The Allocation Length field specifies the number of bytes that the
initiator has allocated for returned data. The Allocation Length is used
to limit the amount of data returned to the initiator.
An Allocation Length of 0 indicates that no data is to be transferred
from the drive to the initiator. The drive terminates the DATA IN phase
when the specified number of bytes have been transferred to the
initiator or when all available data has been transferred, whichever is
less.
Control Field The Control Field is the last byte of every command descriptor block.
Its format is shown in table 73
and described in table 74, and it contains
the Flag and Link bits.
Tech Tip: Flag and Link bits are not supported by the DX-Series
system.
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.
RelAdr Relative Address must be 0 (not supported).
Vendor Specific
Reserved
Flag (0) Link (0)
Field Description