Maxtor ATLAS 10K III Manual download pdf (Page 73)

SCSI Description

5–6 Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives

Bit

Byte

7 6 5 4 3 2 1 0

0 Operation Code

1 Reserved

(MSB)

Logical Block Address

(LBA)

2 - 3 Logical Block Address

(LBA)

(LSB))

4 Transfer Length, Parameter List Length, or Allocation Length

5 Control

NOTE: Reserved fields in CDBs and Parameters have a value of 0; Reserved fields in

states and other parameters sent to an initiator are set to 0.

Figure 5–1 Typical (6-Byte) Command Descriptor Block — Data Format

Table 5–2 Command Descriptor Block — Field Descriptions

Field Description

Operation Code The first byte of a SCSI CDB contains an operation code. The operation

code of the CDB has a Group Code field (bits 7-5) and a Command Code

field (bits 4-0). The 3-bit Group Code field provides for eight groups of

command codes. The 5-bit Command Code field provides for 32

command codes in each group. A total, therefore, of 256 possible

operation codes exist. Operation codes are defined in the SCSI command

standards. The group code for CDBs specified therein correspond to the

length of the command descriptor as below:

Group Code Meaning

0 6-byte commands

1 10-byte commands

2 10-byte commands

3 Reserved

4 16-byte commands

5 12-byte commands

6 Vendor specific

7 Vendor specific

The operation code specifies the command being requested. The list of

supported SCSI commands and their operation codes are contained in

Table 5-1.

(continued)

1 2 ... 68 69 70 71 72 73 74 75 76 77 78 ... 370 371

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Maxtor ATLAS 10K III Manual Page 73