Specifications

Standby mode, the buffer remains enabled, the heads are parked and
the spindle is at rest. The drive accepts all commands, and returns to
Active mode any time disc access is necessary.
Sleep mode. The drive enters Sleep mode when a Sleep Immediate
command has been received from the host. The heads are parked and
the spindle is at rest. The drive leaves Sleep mode when a Hard Reset
or Soft Reset command is sent from the host. After a soft reset has been
received, the drive exits Sleep mode with all current emulation and
translation parameters intact.
Default time delays for both the idle timer and the standby timer are set
by the drive at power-on. In some systems, these delays can be set
manually using the system setup utility. Each time the drive performs an
Active function (read, write or seek), the idle timer is reinitialized, and
begins the countdown from the specified delay time to zero. If the idle
timer reaches zero before any drive activity is required, the drive makes
a transition to Idle mode. After making the transition to Idle mode, the
drive begins the standby timer countdown. If the standby timer reaches
zero before any drive activity is required, the drive makes a transition to
Standby mode. In both Idle and Standby mode, the drive accepts all
commands, and returns to Active mode when disc access is necessary.
In general, after the host issues a command, the drive shifts to the power
management mode that uses the minimum amount of power required to
complete that command (for example, the drive does not start up the
spindle when reading from the cache).
For maximum compatibility, there are multiple command codes for some
power management commands. In such instances, both command
codes perform in an equivalent manner and are treated identically by the
drive.
5.5.1 Check Power Mode command
This command (command codes 98
H
and E5
H
) checks the power mode.
If the drive is in, going to, or recovering from the Standby mode, the drive
sets BSY to 1, sets the Sector Count register to 00
H
, clears BSY, and
then generates an interrupt. If the drive is in the Idle mode, it sets BSY
to 1, sets the Sector Count register to FF
H
, clears BSY, and generates
an interrupt.
5.5.2 Idle command
This command (command codes 97
H
and E3
H
) causes the drive to set
BSY, enter the Idle mode, clear BSY, and generate an interrupt. The
56 ATA Interface Reference Manual, Rev. C