Figure 5. Synchronized Reference Signal Characteristics - Seagate ST15150N - Barracuda 4.3 GB Hard Drive Product Manual

18 ST15150N/ND/W/WD/WC/DC Product Manual, Rev. D
The host can reconfigure the drive any time after power-up to be the
master or a slave by using the Mode Select command on the Rigid Disc
Drive Geometry page. The master provides the reference signal to
which all other drives phase-lock, including the master. There is only
one master per system, and that can be a drive or the host computer.
All drives may be configured as slaves allowing the host to provide the
reference signal.
Each drive also can be configured for the non-synchronized mode in
which it ignores any reference signal that might be present—this is the
default mode as shipped from the factory. The connection of the
synchronized reference signal to the host is required only if the host
provides the reference signal. If the host does not provide the reference
signal, do not connect the host.
Rotational position locking
Note. Mode Select page 4, byte 17, bits 1 and 0.
RPL Description
00b Spindle synchronization is disabled (default value)
01b The target operates as a synchronized-spindle slave
10b The target operates as a synchronized-spindle master
11b The target operates as a synchronized-spindle master control
(not supported by the disc drive)
The Pike LSI on the master drive provides the reference signal (SSREF ).
The index signal generates a 120 Hz signal. The signal is normally false/
negated (nominal 0V) and makes a transition to the true/asserted
(nominal 5V) level to indicate the reference position during the revolu-
tion period. The master and slave drives use the trailing (falling) edge
of the reference signal to phase-lock their spindles. A maximum of 10
seconds is allowed for a slave to synchronize with the reference signal.
Figure 5 shows the characteristics of the reference signal.
1
SSREF +
0
T = 0.0083 seconds
20 microseconds phase error while synchronized

Figure 5. Synchronized reference signal characteristics

T
1.0 µsec min.
1.37 µsec max.
1.0% max