Scanner Interface
The normal SCAN sequence for the scanner is as follows:
Step | Bus phase | Initiator operation | ← → | Target operation |
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1 | Bus Free | Checks Bus Free |
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2 | (Arbitration) | Acquires the right to |
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| use the bus |
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3 | Selection | Selects the target | → |
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| Drives the BSY signal |
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4 | (Message Out) | Selects the logical | → |
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5 | Command | Specifies SCAN | → | Specifies reading |
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6 | Data Out | Specifies the window | → |
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7 | Status |
| ← | Reports the GOOD status |
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8 | Message In |
| ← | Reports message |
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| (Command complete) |
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| Releases the BSY signal |
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9 | Bus Free |
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(1)SCAN command: Command phase (Initiator to Target)
The SCAN command defines reading method for the scanner. The command descriptor block (CDB) is as follows:
7 | 6 |
| 5 | 4 | 3 | 2 | 1 | 0 | ||
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Byte 0 |
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| Operation code X’1B’ |
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1 |
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| Logical unit number |
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| (Reserved) |
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2 |
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3 |
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| (Reserved) |
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4 |
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| Allocation length |
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5 |
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| Control byte |
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∙Transfer length: Byte 4
The transfer length specifies the number of bytes of window data sent during the DATA OUT phase. A 0 means that no data is transferred. This is not an error.
Appendix