Scanner Interface

A.4.14 SCAN

The normal SCAN sequence for the scanner is as follows:

Step

Bus phase

Initiator operation

← →

Target operation

 

 

 

 

 

1

Bus Free

Checks Bus Free

 

 

 

 

 

 

 

2

(Arbitration)

Acquires the right to

 

 

 

 

use the bus

 

 

 

 

 

 

 

3

Selection

Selects the target

 

 

 

 

 

 

 

 

 

 

Drives the BSY signal

 

 

 

 

 

4

(Message Out)

Selects the logical

 

 

 

device

 

 

 

 

 

 

 

5

Command

Specifies SCAN

Specifies reading

 

 

(CDB)

 

 

 

 

 

 

 

6

Data Out

Specifies the window

 

 

 

ID

 

 

 

 

 

 

 

7

Status

 

Reports the GOOD status

 

 

 

 

 

8

Message In

 

Reports message

 

 

 

 

(Command complete)

 

 

 

 

 

 

 

 

 

Releases the BSY signal

 

 

 

 

 

9

Bus Free

 

 

 

 

 

 

 

 

(1)SCAN command: Command phase (Initiator to Target)

The SCAN command defines reading method for the scanner. The command descriptor block (CDB) is as follows:

7

6

 

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

 

Byte 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Operation code X’1B’

 

 

 

1

 

 

 

 

 

 

 

 

 

 

 

Logical unit number

 

 

 

(Reserved)

 

 

2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

 

 

 

 

 

(Reserved)

 

 

 

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Allocation length

 

 

 

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Control byte

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Transfer length: Byte 4

The transfer length specifies the number of bytes of window data sent during the DATA OUT phase. A 0 means that no data is transferred. This is not an error.

Appendix A-104