Product Manual - Hawk 1 Family SCSI-2 (Volume 1), Rev. D
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11.6.4.2 Differential drivers/receivers
Typical differential driver and receiver circuits used by the model ST11200ND 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
+SIGNAL is more positive than -SIGNAL, and a signal is false when -SIGNAL is more positive than +SIG-
NAL. All assigned signals shall be terminated at each end of the cable as shown in Figure 11.6.4-2. 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 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.
* These voltages shall be measured between the output terminal and the SCSI device’s logic ground refer-
ence.
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.
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