A.4 Commands

A.4.4 REQUEST SENSE command

The following table shows the normal sequence of the REQUEST SENSE command when used with this scanner.

Step

Bus phase

Initiator operation

← →

Target operation

 

 

 

 

 

1

BUS FREE

Verifies bus free

 

 

 

 

 

 

 

2

ARBITRATION

Obtains bus-usage

 

 

 

 

right

 

 

 

 

 

 

 

3

SELECTION

Selects target

 

 

 

 

 

 

 

 

 

 

Drives BSY signal

 

 

 

 

 

4

MESSAGE OUT

Selects logical unit

 

 

 

 

 

 

5

COMMAND

Specifies REQUEST

 

 

 

SENSE (CDB)

 

 

 

 

 

 

 

6

DATA IN

 

Reports sense data

 

 

 

 

 

7

STATUS

 

Reports GOOD status

 

 

 

 

 

8

MESSAGE IN

 

Reports message (Command

 

 

 

 

Complete)

 

 

 

 

 

 

 

 

 

Releases BSY signal

 

 

 

 

 

9

BUS FREE

 

 

 

 

 

 

 

 

(1)REQUEST SENSE command: COMMAND phase (initiator target)

The REQUEST SENSE command requests the sense data that shows the status of a logical unit. On receiving this command, the target sets the unit•fs status in the sense data and returns it to the initiator.

The CDB of this command is shown in the following illustration.

7

6

 

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Byte 0

 

 

 

 

 

 

Operation code X’03’

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

 

Logical unit number

 

 

 

(Reserved)

 

 

 

2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

 

 

 

 

 

 

(Reserved)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Allocation length

 

 

 

 

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Control byte

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix A-41