Seagate ST12450W, Product Manual

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56 ST12450W/WD Product Manual, Rev. A
11.7.3.2 Differential drivers/receivers
Typical differential driver and receiver circuits used by ST12450WD drives
are shown in Figure 19. The differential drives have no provisions for
terminator circuits.
Differential signals
All differential interface signals consist of two lines denoted
+
SIGNAL
and –SIGNAL. A signal is true when
+
SIGNAL is more positive than
–SIGNAL, and a signal is false when –SIGNAL is more positive than
+
SIGNAL. All assigned signals must be terminated at each end of the cable.
You must provide external termination for the differential drives.
Output characteristics
Each signal driven by differential interface drives should have the following
output characteristics when measured at the disc drive’s SCSI connector:
Low-level output voltage*
= 2.0V maximum at low-level output current
= 55 milliamps
High-level output voltage*
= 3.0V minimum at high-level output current
= –55 milliamps
Differential voltage
= 1.0V minimum with common-mode voltage ranges
from –7V DC to
+
12V DC
* Measure these voltages between the output terminal and the SCSI
device’s logic ground reference.
The output characteristics must additionally conform to EIA RS-485-1983.