Datasheet
12.10 Delayed Write Function (Vendor Specific)
Delayed Write function is a power saving enhancement whereby the device delays the actual data writing
into the media. When the device is in the power saving mode and the write command
(WRITE SECTORS, WRITE MULTIPLE, or WRITE DMA) comes from the host, the transferred data is not
written into the media immediately. The data is stored in the cache buffer. When the cache buffer be-
comes full, reaches a predefined size, or any command except the write command comes, the operation
of writing the data from the cache buffer into the media begins.
The reason that the Delayed Write function reduces power consumption is as follows. When some write
commands come with a long enough interval the device must exit the power saving mode and reenter the
power saving mode again without a Delayed Write function. If the Delayed Write function is enabled then
power saving mode transition times can be reduced. The additional energy for power saving mode
transition is saved and then the average power consumption of the device is reduced.
The time duration from the write command completion until the media write completion is greatly ex-
tended with the Delayed Write function. If the power for the device is turned off during this time the data
which has not been written to the media is lost. So a command listed in the Write Cache Function section
is issued before the power off to confirm that the whole cached data has been written into the media.
For safety the Delayed Write function is disabled at the Power On Default. The
ENABLE DELAYED WRITE command is issued to the device to enable Delayed Write function at every
POWER ON RESET or HARD RESET. The actions of each reset are shown in Section 12.1 ATA Reset
Response table on page 63.
12.10.1 ENABLE/DISABLE DELAYED WRITE command
The command code FAh with Feature register 07h enables the Delayed Write function.
The command code FAh with Feature register 87h disables the Delayed Write function.
Be careful that even if a Delayed Write function is enabled by command code FAh that a Delayed Write
does not occur when the Write Cache function is disabled.
Hard disk drive specification for DSCM-11000/-10512/-10340
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