Table 5.7 Features Register values (subcommands) and functions
Features Resister  | Function  | 
  | 
  | 
X’D0’  | SMART Read Attribute Values:  | 
  | A device that received this subcommand asserts the BSY bit and saves all the  | 
  | updated attribute values. The device then clears the BSY bit and transfers 512-  | 
  | byte attribute value information to the host.  | 
  | * For information about the format of the attribute value information, see Table 5.8.  | 
X’D1’  | SMART Read Attribute Thresholds:  | 
  | This subcommand is used to transfer   | 
  | data to the host.  | 
  | * For information about the format of the insurance failure threshold value data,  | 
  | see Table 5.9.  | 
X’D2’  | SMART   | 
  | This subcommand is used to enable (SC register !!XX!! 00h) or disable (SC  | 
  | register = 00h) the setting of the automatic saving feature for the device attribute  | 
  | data. The setting is maintained every time the device is turned off and then on.  | 
  | When the automatic saving feature is enabled, the attribute values are saved  | 
  | before the device enters the power saving mode. However, if the failure  | 
  | prediction feature is disabled, the attribute values are not automatically saved.  | 
  | When the device receives this subcommand, it asserts the BSY bit, enables or  | 
  | disables the automatic saving feature, then clears the BSY bit.  | 
X’D3’  | SMART Save Attribute Values:  | 
  | When the device receives this subcommand, it asserts the BSY bit, saves device  | 
  | attribute value data, then clears the BSY bit.  | 
X’D8’  | SMART Enable Operations:  | 
  | This subcommand enables the failure prediction feature. The setting is  | 
  | maintained even when the device is turned off and then on.  | 
  | When the device receives this subcommand, it asserts the BSY bit, enables the  | 
  | failure prediction feature, then clears the BSY bit.  | 
X’D9’  | SMART Disable Operations:  | 
  | This subcommand disables the failure prediction feature. The setting is  | 
  | maintained even when the device is turned off and then on.  | 
  | When the device receives this subcommand, it asserts the BSY bit, disables the  | 
  | failure prediction feature, then clears the BSY bit.  | 
X’DA’ | SMART Return Status:  | 
  | When the device receives this subcommand, it asserts the BSY bit and saves the  | 
  | current device attribute values. Then the device compares the device attribute  | 
  | values with insurance failure threshold values. If there is an attribute value  | 
  | exceeding the threshold, F4h and 2Ch are loaded into the CL and CH registers. If  | 
  | there are no attribute values exceeding the thresholds, 4Fh and C2h are loaded  | 
  | into the CL and CH registers. After the settings for the CL and CH registers have  | 
  | been determined, the device clears the BSY bit  | 
The host must regularly issue the SMART Read Attribute Values subcommand (FR register = D0h), SMART Save Attribute Values subcommand (FR register = D3h), or SMART Return Status subcommand (FR register = DAh) to save the device attribute value data on a medium.
Alternative, the device must issue the SMART 
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