Command Descriptor Block; Figure 5-1 Typical 6-Byte Command Descriptor Block - Data Format - Quantum DLT 8000 Product Manual

SCSI Commands

5.1.2 Command Descriptor Block

An initiator communicates with the drive by sending a 6- or 10-byte Command
Descriptor Block that contains the parameters for the specific command. The SCSI
command's operation code is always the first byte in the Command Descriptor Block and
a control field is the last byte. For some commands, the Command Descriptor Block is
accompanied by a list of parameters sent during the DATA OUT phase. Figure 5–1
shows the format of a typical 6-byte Command Descriptor Block. Table 5–2 contains a
description of the Command Descriptor Block fields.
Bit 7
Byte
0
1 Logical Unit Number
2 - 3
4
5
NOTE: Unless otherwise specified, all reserved bits indicated in the commands are 0.
The Control byte is described on Page 5-6.
Figure 5–1 Typical 6-Byte Command Descriptor Block — Data Format
5-4
6 5
(LUN)
Transfer Length, Parameter List Length, or Allocation Length
Quantum DLT 8000 Tape System
4 3
Operation Code
(MSB)
Logical Block Address
Logical Block Address
(LBA)
Control
2 1
(LBA)
0
(LSB)