5.2 Logical Interface
5.2.3.2 Register - Host to Device
The Register - Host to Device FIS has the following layout:
| 3 | 3 |
| 2 |
| 2 | 2 |
| 2 |
| 2 | 2 | 2 | 2 |
| 2 | 2 | 1 | 1 |
| 1 | 1 | 1 |
| 1 |
| 1 | 1 | 1 | 1 |
| 9 |
| 8 | 7 | 6 |
| 5 | 4 | 3 | 2 |
| 1 | 0 |
| 1 | 0 |
| 9 |
| 8 | 7 |
| 6 |
| 5 | 4 | 3 | 2 |
| 1 | 0 | 9 | 8 |
| 7 | 6 | 5 |
| 4 |
| 3 | 2 | 1 | 0 |
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0 |
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| Features |
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| Command |
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| C | R | R | Reserved (0) |
| FIS Type (27h) |
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1 |
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| Device |
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| LBA High |
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| LBA Mid |
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| LBA Low |
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2 |
| Features (exp) |
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| LBA High (exp) |
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| LBA Mid (exp) |
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| LBA Low (exp) |
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3 |
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| Control |
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| Reserved (0) |
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| Sector Count (exp) |
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| Sector Count |
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4 |
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| Reserved (0) |
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| Reserved (0) |
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| Reserved (0) |
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| Reserved (0) |
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Figure 5.4 Register - Host to Device FIS layout
The host system uses the Register - Host to Device FIS when information in the Register Block is transferred from the host system to the device. This is the mechanism for issuing the ATA command from the host system to the device.
C - To update the Command field, "1" would be set in this field; and to update the Device Control field, "0" would be set in the field.
If both C = 1 and SRST = 1 are set, operation is not guaranteed.