Seagate ST12400N Product Manual page 70

62 Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. B
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11.6.4.2 Differential drivers/receivers
Typical differential driver and receiver circuits used by the model ST12400ND are shown in Figure 11.6.4-2. 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 +SIG-
NAL is more positive than -SIGNAL, and a signal is false when -SIGNAL is more positive than +SIGNAL. All
assigned signals shall be terminated at each end of the cable as shown in Figure 11.6.4-2. Drive user, Systems
integrator or Host equipment manufacturer 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 and the SCSI device's logic ground
reference.
The output characteristics shall additionally conform to EIA RS-485-1983.
Input characteristics
Each signal received by differential interface drives shall have the following input characteristics when measured
at the disc drive SCSI connector:
Input current on either input = +2.0 milliamps maximum (includes both receivers and passive drivers).
This requirement shall 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 shall additionally conform to EIA RS-485-1983.