Mode Sense (10) Command (5Ah) - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
5.13

Mode Sense (10) command (5Ah)

The Mode Sense (10) command provides a means for the drive to report drive operating mode parameters to
the initiator. It is a complementary command to the Mode Select (10) command.
Table 104: Mode Sense (10) command (5Ah)
Bit 7
Byte
0 0
1 Logical Unit Number [1]
2 PCF [3]
3
: Reserved
6
7 (MSB)
8
9 Control [6]
Notes.
[1] The Logical Unit Number must be zero.
[2] A Disable Block Descriptors (DBD) bit of zero indicates that the drive may return zero or more block
descriptors in the returned Mode Sense data, at the drive's discretion. Seagate SCSI-2 products return
one block descriptor if the DBD bit is zero. A DBD bit of one specifies that the drive shall not return any
block descriptors in the returned Mode Sense data. Byte 3 of the Mode Sense header contains 00h to
indicate a block descriptor length of zero.
[3] The content of mode parameter bytes is determined by the value of the PCF (Page Control Field) bits
specified in CDB byte 2, bits 6 and 7. The drive shall return the same Page Length for each supported
page regardless of the value of PCF. The PCF field is defined in Table 105.
Table 105: Page Control Field bits affect on mode parameters returned
Bit 7 Bit 6
0 0 Return Current values. The Current values are the values currently being used by the drive
to control its operation. After a Power On Reset, a hard Reset, or a Bus Device Reset mes-
sage the Current values are equal to the Saved values (if Saved values can be retrieved) or
the Default values (if Saved values cannot be retrieved). The Current value of a parameter is
updated by a Mode Select command if the Mode Select command ends with Good status
returned.
0 1 Return Changeable values. The changeable values of any page is a mask that indicates the
parameters that shall be changed via a Mode Select command and the parameters that
shall not. Each returned parameter byte shall contain ones where a field or bit may be
changed and zeros where a field or bit may not be changed.
1 0 Return Default values. The Default values are the values to which the drive sets the Current
values after a reset condition unless valid Saved values are available.
1 1 Return Saved values. The saved values are the values the drive stores in nonvolatile mem-
ory. The Saved values of any changeable parameter can be set to new values via a Mode
Select command with the SMP bit set to one. For non-changeable parameters, the Default
value is used.
The Block descriptor contains its normal values regardless of the value of the PCF. Unsupported fields or
bits within a page are returned as zeros for all PCF values.
6 5
1 0
Reserved
Allocation Length [5]
4 3
1 1
DBD [2]
Page Code [4]
2 1
0 1
Reserved
(LSB)
149
0
0