Scanner Interface

A.4.6 TEST UNIT READY command

The following table shows the normal sequence of the TEST UNIT READY 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 TEST UNIT

 

 

 

READY (CDB)

 

 

 

 

 

 

 

6

STATUS

 

Reports GOOD status

 

 

 

 

 

7

MESSAGE IN

 

Reports message (Command

 

 

 

 

Complete)

 

 

 

 

 

 

 

 

 

Releases BSY signal

 

 

 

 

 

8

BUS FREE

 

 

 

 

 

 

 

 

(1)TEST UNIT READY command: COMMAND phase (initiator target)

The TEST UNIT READY command checks whether a logical unit is ready. This command does not request self-test. The acknowledgment of this command reported using the status and sense data.

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

7

6

 

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Byte 0

 

 

 

 

 

 

Operation code X’00’

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Logical unit number

 

 

 

(Reserved)

 

 

 

2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(Reserved)

 

 

 

 

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Control byte

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix A-48