Seagate ST12400N Product Manual page 25

Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. B
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SCSI Interface Factors
The Rotational Position Locking (RPL) field in byte 17 (bits 0 and 1) of the Rigid Disc Drive Geometry mode
parameters page (page 04h) is used for enabling/disabling spindle synchronization mode*. If the target fails to
achieve synchronization, it shall create a unit attention to all initiators. The sense key shall be set to UNIT ATTEN-
TION and the additional sense code set to RPL STATUS CHANGE. However, in automatic arbitration mode,
UNIT ATTENTION and the RPL STATUS CHANGE is not set.
If subsequent to achieving synchronization the target detects a change of synchronization:
1) and, if the logical unit is not presently executing an I/O process for the initiator, the target shall create a unit
attention condition. The sense key shall be set to UNIT ATTENTION and the additional sense code set to
RPL STATUS CHANGE.
2) and, if the logical unit is presently executing an I/O process and no other error occurs, the target shall return
CHECK CONDITION status. The sense key shall be set to RECOVERED ERROR if the target is able to
complete the I/O process or HARDWARE ERROR if the target is unable to complete the I/O process. The
additional sense code is set to RPL STATUS CHANGE.
The drive may be operated with a rotational skew when synchronized. The rotational skew is applied in the
retarded direction (lagging the synchronized spindle master control). A rotational offset of up to 255/256 of a
revolution lagging may be selected. The amount of offset is selected by using the Mode Select command, Rigid
Disc Drive Geometry page (page 04), byte 18*. The value in byte 18 (0 - FFh) is the numerator of a fractional
multiplier that has 256 as the denominator. For example, 40h selects 40h/FFh or 1/4 of a revolution lagging skew,
80h selects 1/2 revolution lagging skew and etc. Since the drive supports all offset values from 0 to 255, values
sent by the initiator are not rounded off. The drive translation of the digital offset values to physical rotational
offsets results in offset values whose phase error lies within the + or - 20 usec phase error with respect to the
supplied 90.18 Hz reference signal.
The drive does not have the capability to adjust the rotational offset value requested by the initiator to a physical
offset in the drive that corresponds in any way to sector boundaries or changes in ZBR zones. Such correspon-
dences or changes, if required, must be formulated by the initiator in order for it to calculate the value of offset it
sends to the drive.
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*SCSI Interface Product Manual P/N 77738479.
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