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Western Digital Hard Disk Drive OEM Specification
11.51.1
SMART Subcommand
In order to select a subcommand the host must write the subcommand code to the device’s Features Register before
issuing the SMART Function Set command. The subcommands and their respective codes are listed below.
Code
Subcommand
D0h
SMART Read Attribute Values
D1h
SMART Read Attribute Thresholds
D2h
SMART Enable/Disable Attribute Autosave
D3h
SMART Save Attribute Values
D4h
SMART Execute Off-line Immediate
D5h
SMART Read Log Sector
D6h
SMART Write Log Sector
D8h
SMART Enable Operations
D9h
SMART Disable Operations
DAh
SMART Return Status
DBh
SMART Enable/Disable Automatic Off-Line
11.51.1.1
SMART Read Attribute Values (Subcommand D0h)
This subcommand returns the device’s Attribute Values to the host. Upon receipt of the SMART Read Attribute
Values subcommand from the host, the device saves any updated Attribute Values to the Attribute Data sectors, and
then transfers the 512 bytes of Attribute Value information to the host.
11.51.1.2
SMART Read Attribute Thresholds (Subcommand D1h)
This subcommand returns the device’s Attribute Thresholds to the host. Upon receipt of the SMART Read Attribute
Thresholds subcommand from the host, the device reads the Attribute Thresholds from the Attribute Thres hold
sectors, and then transfers the 512 bytes of Attribute Thresholds information to the host.
11.51.1.3
SMART Enable/Disable Attribute Autosave
(Subcommand D2h)
This subcommand Enables and Disables the Attribute Autosave feature of the device. The SMART Enable/Disable
Attribute Autosave subcommand either allows the device to automatically save its updated Attribute Values to the
Attribute Data Sector periodically; or this subcommand causes the Autosave feature to be disabled. The state of the
Attribute Autosave feature (either enabled or disabled) will be preserved by the device across power cycle.
A value of 00h written by the host into the device’s Sector Count Register before issuing the SMART Enable/Disable
Attribute Autosave subcommand will cause this feature to be disabled. Disabling this feature does not preclude the
device from saving Attribute Values to the Attribute Data sectors during some other normal operation such as during
a power-up or power-down.
A value of F1h written by the host into the device’s Sector Count Register before issuing the SMART Enable/Disable
Attribute Autosave subcommand will cause this feature to be enabled. Any other non-zero value written by the host
into this register before issuing the SMART Enable/Disable Attribute Autosave subcommand will not change the
current Autosave status but the device will respond with the error code specified in Table 242.
The SMART Disable
Operations subcommand disables the Autosave feature along with the device’s SMART
operations.
Upon the receipt of the subcommand from the host, the device asserts BSY, Enables or Disables the Autosave
feature, clears BSY and asserts INTRQ.
