4.4.6TEST UNIT READY command
The following table shows the normal sequence of the TEST UNIT READY 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 TEST | Æ |
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| UNIT READY |
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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)TEST UNIT READY command: COMMAND phase (initiator Æ target)
The TEST UNIT READY command checks whether a logical unit is ready. This command does not request self>test. The acknowledgment of this command reported using the status and sense data.
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©00 |
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1 |
| Logical unit number |
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2 |
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3 |
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5 |
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| Control |
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4 $ 36