Differential Drivers/Receivers; Figure 13. Hvd Output Signals - Seagate ST39173N Product Manual

Barracuda 9LP Product Manual, Rev. C
[2] ANSI SCSI compatible circuits.
[3] Total interface cable length should not exceed that specified in ANSI Standard X3T10/1142D.
[4] Source of drive terminator power is an active circuit which has an input source voltage selected by jumper
plug TP. See Figure 7d. Applies to "N" and "W" models.
[5] Interface signal levels and logical sense at the drive I/O connector for "N," "W," and "WC" models are
defined as follows:
Vil (low-level input voltage) = 1.0 V maximum (signal true); minimum = Vss – 0.5 V.
Vih (high-level input voltage) = 1.9 V minimum (signal false); maximum = Vdd +0.5V.
Vihys (Input Hysteresis) = 425 mV minimum
9.7.2

Differential drivers/receivers

9.7.2.1 High-voltage differential (HVD) alternative
HVD drivers and receivers are used by the "WD" model. Typical circuits are shown in Figures 13 and 14. The
drive has no provisions for terminator circuits on differential I/O drives. When the "DIFFSENS" interface line is
between 2.4 V and 5.5 V, it selects HVD interface operation.
HVD 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.
Drive user or systems integrator must provide some external means of termination.
Output characteristics
Each signal driven by differential interface drives shall have the following output characteristics when measured
at the disc drive SCSI connector:
Low-level output voltage* = 2.0 V maximum at Low-level output current = 55 milliamps.
High-level output voltage* = 3.0 V minimum at High-level output current = –55 milliamps
Differential voltage = 1.0 V minimum with common-mode voltage ranges from –7 V dc to +12 V dc.
*These voltages shall be measured between the output terminal (either + signal or – signal) and the SCSI
device's logic ground reference.
The output characteristics shall additionally conform to EIA RS-485-1983.
HVD Differential
Driver
Signal +
Signal –
HVD Differential
Driver
Signal +
Signal –
|V | = 1V
0
Figure 13. HVD output signals
Input characteristics
Each signal received by differential interface drives shall have the following input characteristics when mea-
sured at the disc drive SCSI connector:
Input current on either input = +2.0 milliamps maximum (includes both receivers and passive drivers).
3V –55ma
2V +55ma
2V +55ma
3V –55ma
V = True / Logic 1 / Assertion
0
V = False / Logic 0 / Negation
0
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