Seagate ST11200N Product Manual page 26

18 Product Manual - Hawk 1 Family SCSI-2 (Volume 1), Rev. D
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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 set 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/100h 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 - 50 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 correspondences 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.