Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E 169
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5.2.1.11
Start Stop Unit Command (1Bh)
Table 5.2.1-32. Start/Stop Unit Command
Bit
7
6
5
4
3
2
1
0
Byte(s)
0
0
0
0
1
1
0
1
1
1
Logical Unit No.
IMMED
0
0
0
0
0
0
0
[1]
2
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
4
Start
0
0
0
0
0
0
0
[2]
5
0
0
0
0
0
0 Flag Link [3]
The Start/Stop Unit command requests that the target enable the logical unit for further operations (start), or
stop spindle rotation (stop).
Notes.
[1] An Immed bit of zero indicates that status shall be returned after the operation is completed. If the Immed
bit is a one status is returned as soon as the operation is initiated.
[2] When the Start bit is a 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 the drive Product Manual.
[3] See “Control Byte” paragraph 4.2.6.
The disc drive is able to execute the following commands when the drive spindle is not rotating, or in a
simulated stopped condition.
Test Unit Ready
Motor Start
Request Sense
Receive Diagnostic Results
Inquiry
Write Data Buffer
Reserve
Read Data Buffer
Release
The remaining commands (see section “SCSI Interface commands supported” in drive Product Manual for
list of all commands supported) cannot be executed until after the drive has spindled up. If the disc 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 disc drive disconnects when a Start Unit procedure is com-
manded, and reconnects when the unit is up to speed and Ready or when operation is initiated if the “Immed”
bit is one.
