4.4.2RELEASE UNIT command
The following table shows the normal sequence of the RESERVE UNIT command when used with this scanner.
Step | Bus phase | Initiator operation | ¨ Æ | Target operation |
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1 | BUS FREE | Verifies bus free |
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2 | ARBITRATION | Obtains bus>usage |
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| right |
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3 | SELECTION | Selects target | Æ |
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| Drives BSY signal |
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4 | MESSAGE OUT | Selects logical unit | Æ |
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5 | COMMAND | Specifies | Æ |
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| RELEASE UNIT |
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6 | STATUS |
| ¨ | Reports GOOD status |
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7 | MESSAGE IN |
| ¨ | Reports message (Command |
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| Complete) |
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| Releases BSY signal |
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8 | BUS FREE |
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(1)RELEASE UNIT command: COMMAND phase (initiator Æ 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 |
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Byte 0 |
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| Operation code X©17 |
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| Logical unit number | TP |
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3 |
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5 |
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| Control byte |
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4 $ 24