Start/Stop Unit Command (1Bh) - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
5.45

Start/Stop Unit command (1Bh)

The Start/Stop Unit command requests that the target enable the logical unit for further operations (start) or
stop spindle rotation (stop).
The drive is able to execute the following commands when the drive spindle is not rotating, or in a simulated
stopped condition:
Test Unit Ready
Request Sense
Inquiry
Reserve
Release
Motor Start
Receive Diagnostic Results
Write Data Buffer
Read Data Buffer
The remaining commands (see individual drive's Product Manual, Volume 1, SCSI interface commands sup-
ported section, for a list of all commands supported) cannot be executed until after the drive has spindled up. If
the drive receives one of these commands before it can be executed, a Check Condition status is returned
(with sense key of Not Ready).
For systems that support disconnection, the drive disconnects when a Start Unit procedure is commanded,
and reconnects when the unit is up to speed and Ready or when operation is initiated if the Immed bit is one.
Table 167: Start/Stop Unit command (1Bh)
Bit 7
Byte
0 0
1 0
Logical Unit Number
2 0
3 0
4 0
5 0
Notes.
[1] An Immediate (Immed) bit of zero indicates that status shall be returned after the operation is completed.
If the Immed bit is one, status is returned as soon as the operation is initiated.
[2] When the Start bit is one, this requests that the logical unit be made ready for use. If the Start bit is zero
(requesting that the unit be stopped), the request causes the drive to either actually stop the spindle or to
simulate the drive spindle stopped condition. In this latter situation, the drive spindle actually continues to
spin and the drive reports Not Ready in response to media access commands. Power consumption is as
when in idle mode. The type of stop implemented is given in individual drive's Product Manual, Volume 1.
[3] See "Control byte," paragraph 4.2.6.
6 5
0 0
0 0
0 0
0 0
0 0
0 0
4 3
1 1
0 0
0 0
0 0
0 0
0 0
2 1
0 1
0 0
Immed [1]
0 0
0 0
0 0 Start [2]
0 Flag [3] Link [3]
209
0
1
0
0