Differential Drivers/Receivers - Seagate ST34501N Product Manual

Cheetah 4LP Product Manual, Rev. B 65
9.7.2

Differential drivers/receivers

Differential drivers and receivers are used by the "WD" and "DC" models. Typical circuits are shown in Figure
21. The drive has no provisions for terminator circuits on differential I/O drives.
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.
Drive user or systems integrator must provide some external means of termination.
Output characteristics
Each signal driven by differential interface drives should have the following output characteristics when mea-
sured 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.
*Measure these voltages between the output terminal and the SCSI device's logic ground reference.
The output characteristics should additionally conform to EIA RS-485-1983.
Input characteristics
Each signal received by differential interface drives should 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).
This requirement should be met with the input voltage varying between –7 V DC and +12 V DC, with power on
or off, and with the hysteresis equaling 35 mV, minimum.
The input characteristics should additionally conform to EIA RS-485-1983.