Figure 8. External Spindle Clock Timing Diagram - Seagate ST3285N Product Manual

ST3655 Family SCSI Drives Product Manual, Rev. A
The spindle-synchronization characteristics can be controlled by the
Mode Select command using the RPL bits in byte 17 of the Rigid Disc
Geometry page.
In the default mode, all drives arbitrate during startup to see which drive
will be the synchronized master. When the drives are calibrating their
heads, they each check for a reference signal pulse. The drive that
becomes ready first checks for the reference signal, and when it does
not detect a pulse, it takes over as the master and begins sending
reference pulses. All other drives synchronize their spindles to the
reference signal as they in turn become ready.
T2
Spindle clock
Internal index
T3

Figure 8. External spindle clock timing diagram

T1 Spindle clock period
T2 Duty cycle
T3 Spindle clock leading edge to
index leading edge
T1
13.34 msec ± 0.5%
0.5 µsec min
500 µsec max
0 µsec ± 250 µsec
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