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A.4 Commands
Appendix A-41
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.
1
Byte 0
5
4
3
2
Operation code X’03’
Logical unit number
(Reserved)
(Reserved)
Control byte
7
6
5
4
3
2
1
0
Allocation length