The Advanced Power Management feature consists of:
• A Set Features subcommand code to enable Advanced Power Management
• A Set Features subcommand code to disable Advanced Power Management
• Identify Data bits to indicate that the feature is supported and enabled
• An Identify Data byte to indicate the current power management level.
Set Features Subcommand Code 05h, Enable Advanced Power Management
Subcommand code 05h allows the host to enable Advanced Power Management. To enable Advanced
Power management the host systems writes the sector count register with the desired Advanced power
management level and then executes a Set Features command with subcode 05h. The power management
level is a scale from the lowest power consumption setting of 01h to the maximum performance level of FEh,
see table 1.
Table 1− Advanced Power Management Levels
Mode Sector Count
Intermediate Power Management Levels
81h - FDh
Minimum Power Consumption Without
Intermediate Power Management Levels With
02h - 7Fh
Minimum Power Consumption With Standby
Device performance increases with increasing power management levels. Device power consumption
increases with increasing power management levels. The power management levels may contain discrete
bands. For example, a device may implement one power management method from level 80h to A0h and a
higher performance, higher power consumption method from level A1h to FEh. Advanced Power
Management Levels 80h and higher do not permit the device to spin down to save power.
Set Features Subcommand Code 85h, Disable Advanced Power Management
Set Feature Subcommand 85H disables Advanced Power Management. Subcommand 85h may not be
implemented on all devices which implement Set Feature subcommand 05h.
Identify Data Support for Advanced Power Management
Identify Device Word 83 bit 3 indicates that Advanced Power Management is supported
Identify Device Word 86 bit 3 indicates that Advanced Power Management is Enabled
Identify Device Word 91 bits (0:7) contain the current Advanced Power Management level setting
Other Advanced Power Management Considerations
Advanced Power Management is independent of the standby timer setting. If both Advanced Power
Management and the standby timer are set the device will go to the standby state when the timer times out or
the device’s Advanced Power Management algorithm indicates that it is time to enter standby.