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Command Specifications
4.1.9 START/STOP UNIT (1B)
Bit
Byte
7 6 5 4 3 2 1 0
0 X'1B'
1 0 0 0 0 0 0 0 Immed
2 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 LoEj Start
5 0 0 0 0 0 0 0 0
This command controls the power condition of the disk drive. For the power
condition, see Chapter 2, "Power Condition."
The control of the power condition is performed with the Start bit in bit 0 of the
CDB byte 4.
Issuing this command with the Start bit set to "0" transits from the power
condition state to the Stopped state. Meanwhile, setting the Start bit to "1"
transforms the power condition state from the Stopped state to the Active_Wait
state. Setting the Start bit to "1" does not transform the power condition state
when it is in a state other than the Stopped state.
Bit 1 (LoEj (load/eject) of byte 4 of the CDB is the exclusive bit which controls
devices with replaceable recording media, and it has no meaning for the HDD.
The HDD disregards the value specified in this bit and controls the Power
Condition in accordance with the "Start" bit only.
Depending on the value specified in the "Immed (immediate)" bit, bit 0 of CDB
byte 1, the timing of completion (status byte report) of this command differs as
shown below.
a. In the case of the start specification ("Start" bit = "1")
− When the Immed bit is "1," the power condition state becomes
Active_Wait, the GOOD status is reported, and command execution is
completed.
178 C141-C013