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4.4.2 RELEASE UNIT command
The following table shows the normal sequence of the RESERVE UNIT command when used with this
scanner.
Table 4-9 RELEASE UNIT 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 Selects local unit →
OUT
5 COMMAND Specifies RELEASE →
UNIT (CDB)
6 STATUS ← Reports GOOD status
7 MESSAGE IN ← Reports message (Command Complete)
Releases BSY signal
8 BUSFREE
4.4.2.1 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.
7 6 5 4 3 2 1 0
Operation code X'17'
Logical unit number TP TPID (Reserved)
(Reserved)
Control byte
(a) TP (third party): Byte 1
Byte 0
1
2
3
4
5