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44
Current values are volatile values currently being used by the drive to control its operation. A Mode Select
command can be used to change these values (only those that are changeable). Originally, they are installed
from Saved or Default values after a power on reset, hard reset, or Bus Device Reset message.
Changeable values form a bit mask, stored in nonvolatile memory, that dictates which of the Current values
and Saved values can be changed by a Mode Select command. A "one" allows a change to a corresponding
bit; a "zero" allows no change. For example, in Table 9 refer to Mode page 01, in the row titled "CHG". These
are hex numbers representing the changeable values for Mode page 01. Note that bytes 04, 05, 06, and 07 are
not changeable, because those fields are all zeros. If some changeable code had a hex value EF, that equates
to the binary pattern 1110 1111. If there is a zero in any bit position in the field, it means that bit is not change-
able. Bits 7, 6, 5, 3, 2, 1, and 0 are changeable, because those bits are all ones. Bit 4 is not changeable.
Though the drive always reports non-zero values in bytes 00 and 01, those particular bytes are never change-
able.
The Changeable values list can only be changed by downloading new firmware into the flash EPROM.
On standard OEM drives the Saved values are taken from the Default values list and stored into the Saved val-
ues storage location on the media prior to shipping.
When a drive is powered up, it takes Saved values from the media and stores them to the Current values stor-
age in volatile memory. It is not possible to change the Current values (or the saved values) with a Mode Select
command before the drive is up to speed and is "ready." An attempt to do so results in a "Check Condition" sta-
tus being returned.
Note.
Because there may be several different versions of drive control firmware in the total population of
drives in the field, the Mode Sense values given in the following tables may not exactly match those of
some drives.
Cheetah 4LP Product Manual, Rev. B
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