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4.4.4 REQUEST SENSE command
The following table shows the normal sequence of the REQUEST SENSE command when used with this scanner.
Table 4-11 REQUEST SENSE command
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
4.4.4.1 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's 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
Operation code X'03'
Logical unit number (Reserved)
Allocation length
Control byte
Byte 0
1
2
3
4
5
(Reserved)