Seagate ST3285N, Product Manual

Page: 58 / 151

3.4.10 Mode Select command (15
H
)
The Mode Select command allows the initiator to change parameters
stored in the mode pages. The mode pages are described in Appendix C.
The drive stores four copies of each mode page:
•
Current values copy. This copy contains the parameter values the
drive is using to control its operation. After a power-on reset, hard reset
or bus device reset, the current values are equal to the saved values
if the saved values can be retrieved, or the default values if the saved
values cannot be retrieved.
•
Changeable values copy. This copy does not actually contain any
parameters. Instead, it contains a map of each mode page indicating
which parameter values are changeable by the initiator. If a bit
contains a 1, the corresponding value in the mode page is change-
able. If a bit contains a 0, the corresponding value in the mode page
is not changeable. The changeability values for each bit of each mode
page are listed in Appendix C with the default values.
•
Default values copy. This copy contains the parameter values the
drive used as its current values when it was manufactured. The drive
defaults to these values after a reset condition, unless valid saved
values are available. The default values are listed in Appendix C.
•
Saved values copy. The saved values are the values the drive stores
on the disc. If the parameter is changeable, these values can be set
using a Mode Select command. If the parameter is not changeable,
the default values are always used.
The drive has one set of mode parameters for each initiator on the SCSI
bus. If the initiator that issued the Mode Select command changes a
parameter that applies to another initiator, the drive generates a sense
key of
unit attention with an additional sense of mode parameters
changed (26
H
) for all the other initiators. The sense keys and additional
sense codes are discussed in Appendix B.
Before sending any Mode Select commands, the initiator should send a
Mode Sense command requesting that the drive return all pages with
changeable values. The initiator uses this information to determine which
pages are supported, the proper length for those pages, and which
parameters in those pages can be changed for that logical unit.
When the drive receives the Mode Select command, it updates the
savable parameters with the current values included in the Mode Select
command. After the drive saves the parameters, the drive reports a good
status. The drive verifies only mode select data that is defined as
changeable.
48 ST3655 Family SCSI Drives Product Manual, Rev. A