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M2488 PRODUCT GUIDE MEDIA CHANGER COMMANDS
March 1997 CG00000-011503 REV. A 6-7
For both an ACL or a FACL, the target will perform the MODE SELECT command even if the
Medium Changer LUN is NOT READY.
If the target completes a MODE SELECT command successfully, it generates a Unit Attention
Condition for all initiators except the one that issued the MODE SELECT command. The addi-
tional sense code reported for the Unit Attention Condition is MODE PARAMETERS
CHANGED.
The Unit Attention/Mode Parameters Changed sense data will be reported to other initiators after a
Mode Select command only if the setting of at least one parameter was actually changed from its
previous setting. Therefore, issuing a Mode Select command with parameters that are the same as
the current parameters will not result in any change or the reporting of a Unit Attention to other
initiators.
To ensure that the MODE SELECT command performs the desired operations, it is strongly rec-
ommended that the initiator adhere to the following steps:
1. issue a MODE SENSE command requesting the target to return all Changeable Values (PC
field 01b and Page Code 3Fh in byte two of the MODE SENSE CDB) and preserve the
“changeable” values,
2. issue a MODE SENSE command requesting the target to return all Current Values (PC field
00b and Page Code 3Fh in byte two of the MODE SENSE CDB) and preserve the “current”
values,
3. perform a bitwise AND operation of the “current” values with the one’s complement of the
“changeable” values, (this step is important because the target will not accept the command if
any non-changeable field is set to a value other than the “current” value)
4. make further desired changes to bytes which are changeable,
5. make sure that the PS bit in every mode page is 0 (the MODE SENSE command will report a 1
in the PS bit, but a MODE SELECT command will fail if mode pages are sent with the PS bit
set to 1),
6. issue a MODE SELECT command, sending these parameters,
A PF bit of 0 or 1 both indicate that the Mode Select parameters are structured as pages of related
parameters as defined by the ANSI standard.
Pages which can be saved are identified by the Parameter Savable (PS) bit that is returned in the
page header by the MODE SENSE command. If the PS bit is set in the MODE SENSE data, the
page can be saved by issuing a MODE SELECT command with the SP bit set. Once a MODE
SELECT command with an SP bit of one is completed successfully, the parameters set during that
command become the “saved parameters”. The “saved parameters” become the active or “current
parameters” until another MODE SELECT command is completed. If the new MODE SELECT
command has an SP bit of 0, the newly set parameters become the “current parameters” and
remain in effect until any of the following occurs:
a) a new MODE SELECT command is successfully performed,
b) a RESET CONDITION is detected,
c) a power-on cycle is performed, or
d) a BUS DEVICE RESET message is received,
in which case the “saved parameters” are restored as the active or “current parameters”. If the
new MODE SELECT command has an SP bit of 1, the newly set parameters become the
“saved parameters” as well as the active or “current parameters”. Therefore, following any of
the conditions described in b) through d) above, the newly set “saved parameters” will be
restored as the “current parameters”.