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Appendix A-24
A.4.2 RELEASE UNIT command
The following table shows the normal sequence of the RESERVE UNIT 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 RELEASE
UNIT (CDB)
→
6 STATUS
←
Reports GOOD status
7 MESSAGE IN
←
Reports message (Command
Complete)
Releases BSY signal
8 BUS FREE
(1) RELEASE UNIT command: COMMAND phase (initiator → target)
The RELEASE UNIT command releases a reserved status. If this command comes from an
initiator that has not declared reservation, the target ignores the command and responds with
the GOOD status (the reserved status is not released).
The CDB of this command is shown in the following illustration.
Byte 0
Operation code X’17’
2
3
4
5
TP
TPID
(Reserved)
(Reserved)
Control byte
1
7
6
5
4
3
2
1
0
Logical unit number