Power-Off Considerations; Load/Unload; Emergency Unload; Figure 61. Device Behavior By Ata Commands - Hitachi IC25N040ATCS04-0 - Travelstar 40GN 40GB UDMA/100 4200RPM 2MB 2.5" IDE Hard Drive Specifications

11.4 Power-off considerations

11.4.1 Load/Unload

Load/Unload is a functional mechanism of the hard disk drive. It is controlled by the drive microcode.
Specifically, unloading of the heads is invoked by the following commands.
Command
Standby
Standby Immediate
Sleep
Reset
Soft Reset
Hard Reset
UL = unload
Comp = complete
Rdy = interface ready
(*1) Load/Unload condition is not changed by Soft Reset

Figure 61. Device behavior by ATA commands.

Load/unload is also invoked as one of the idle modes of the drive.
The specified start/stop life of the product assumes that load/unload is operated normally, NOT in emer-
gency mode.

11.4.2 Emergency unload

When the drive power is interrupted with the heads still loaded, the microcode cannot operate and the
normal 5V power is unavailable to unload the heads. In this case, normal unload is not possible, so the
heads are unloaded by routing the back EMF of the spinning motor to the voice coil. The actuator velocity
is greater than the normal case, and the unload process is inherently less controllable without a normal
seek current profile.
Emergency unload is intended to be invoked in rare situations. Because this operation is inherently uncon-
trolled, it is more mechanically stressful than a normal unload.
A single emergency unload operation is more stressful than 100 normal unloads. Use of emergency un-
load reduces the start/stop life of the drive at a rate at least 100 times faster than that of normal unload
and may damage the drive.
Response
Response
Hitachi Travelstar 60GH & 40GN hard disk drive specifications
UL -> Comp.
UL -> Comp.
UL -> Comp.
Rdy (*1)
UL -> Rdy
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