SCSI Mode Sense Command
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The SCSI Mode Sense command is used to obtain current device information from mode pages in a SCSI target device. There are two different versions of the command, a 6 byte version and a 10 byte version.
The CDB structure for the Mode Sense(6) command is:
| bit→ ↓byte |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0 | Operation code = 1Ah | |||||||
| 1 | LUN | Reserved | DBD | Reserved | ||||
| 2 | PC | Page code | ||||||
| 3 | Reserved | |||||||
| 4 | Allocation length | |||||||
| 5 | Control | |||||||
The CDB structure for the Mode Sense(10) command is:
| bit→ ↓byte |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0 | Operation code = 5Ah | |||||||
| 1 | LUN | Reserved | DBD | Reserved | ||||
| 2 | PC | Page code | ||||||
| 3 | Reserved | |||||||
| 4 | Reserved | |||||||
| 5 | Reserved | |||||||
| 6 | Reserved | |||||||
| 7–8 | Allocation length | |||||||
| 9 | Control | |||||||
The special control fields in the CDB have the following meaning:
- DBD - Disable Block Descriptors - if "1" then the target must not return any block descriptors
- PC - Page control -
- 00 - return current values
- 01 - return changeable values
- 10 - return default values
- 11 - return saved values
- Page Code - see the separate Wikipedia page for a list of mode pages
