Seagate Barracuda ST11950N, Product Manual

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50 Barracuda 1 and 2 Product Manual, Rev. C
10.2 Synchronized spindles interface
The synchronized spindles interface (SSI) allows several drives operating
from the same host to operate their spindles at a synchronized rotational rate.
Details of the electrical and physical interfaces follow in Section 10.2.1. The
system operation is described in Section 5.7.
10.2.1 Electrical description
The electrical interface consists of one digital TTL reference index signal and
ground. The reference index signal (SSREF+) is an output if the drive is
configured as a master and is an input otherwise. The reference index signal
is connected from drive to drive in a daisy-chain fashion as shown in Figure 4.
10.2.1.1 Drivers and receivers
Figure 20 shows a diagram of the driver/receiver circuit. The driver circuits
have the following electrical specifications:
Negated (false): 0.0V to +0.4V @ I = –24 mA (max)
Asserted (true):
+2.24V to +5.25V @ I = +250 µA
Driver Receiver
2.21K Ohm
SSREF +
GND
Main PWA
J4 - 1 (N/ND Drives)
J5 - 11 (W/WD Drives)
+5V
J4 - 2 (N/ND Drives)
J5 - 12 (W/WD Drives)
Open
Collector
Figure 20. SCSI reference index signal driver/receiver combination