Filter
Top Products
Scanner Interface
Appendix A-104
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
(CDB)
→
Specifies reading
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:
• 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.
Byte 0
1
2
3
4
5
Operation code X’1B’
Logical unit number
7
6
5
4
3
2
1
0
(Reserved)
Control byte
(Reserved)
Allocation length