Seagate Elite 9, Руководство по эксплуатации продукта

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Elite 9 Product Manual, Rev. C 57
11.7.3.2 Differential drivers and receivers
Typical differential driver and receiver circuits used by ST410800ND/WD
drives are shown in Figure 18.
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.
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.
Input characteristics
Each signal received by differential interface drives should have the following
input characteristics when measured at the disc drive’s SCSI connector:
Input current on either input
=
+
2.0 milliamps maximum
(includes receivers and passive drivers)
This requirement is met with the input voltage varying between
−
7V DC and
+
12V DC, with power on or off, and with the hysteresis equaling 35 mV
minimum.
The input characteristics must additionally conform to EIA RS-485-1983.
DE
RE
LSI
XCVR
1
1
R 2
+5V
+5V
5.6K
Transmit/Receive
Enable [1]
Transmit or
Receive
Signal [2]
[3]
[4]
Figure 18. Typical differential I/O line transmitter/receiver and terminators